Fasteners for Kit Cars - A Buyer’s Guide

The average car contains between 3000 and 5000 fasteners, from button head screws to nyloc nuts. It's easy to overlook correct fastener selection when dealing with so many, but they're critical to both safety and the longevity of the vehicle.

Accu are no strangers to automotive fasteners, with a track record of supplying motorsports hardware for everything from top-flight formula race teams to rebuilds of iconic rally cars and pole-position student race teams. With their guidance, we've put together this guide on choosing the right fasteners for your kit car build.  

We'll cover everything from material selection to which components work best in different areas of the build. We'll also cover options that go beyond the basics, from aesthetics to protection against vibration loosening. Throughout, you’ll find links to the Accu components featured, making it easier to quickly fulfil your bill of materials and source the precision fasteners you need to build your own kit car.

Contents:

• Material Selection for Kit Car Components

• Specialist Materials

• Material Pairings and Galvanic Corrosion

• Kit Car Fasteners by Build Area

• Anti-vibration and Locking Strategies

• Key Takeaways

• FAQs

Material Selection for Kit Car Components

There's a staggering array of fastener materials available for use in your kit car build. Choosing the right material type comes down to the purpose of each joint and the environment it's going to be exposed to. Three materials cover essentially every application on a kit car, so we've broken them down below with clear reasons behind each. We’ve also outlined some additional exotic materials that could provide advantages depending on the ultimate goal of your build.

A2 Stainless Steel

A2 stainless steel offers a tensile strength of around 700 Megapascal (MPa), which is more than sufficient for body panel fixings, interior trim and non-structural brackets. It resists corrosion from road spray, cleaning chemicals and general atmospheric exposure without any surface treatment, which means no plating to chip or flake over time.

That last point is more important than you might realise. Plated carbon steel fasteners can look fine initially, but once the plating is compromised by a stone chip, a scratch from a spanner or simple wear and tear, the exposed steel beneath corrodes rapidly. 

The majority of Accu's screw, nut and washer range is available in A2, making it the natural default for most of the fixings on your kit car build.

A4 (Marine Grade) Stainless Steel 

A4 (marine grade) stainless steel contains molybdenum, which gives it significantly better resistance to corrosion issues like chloride-induced pitting when compared to A2 stainless steel. In practical terms, that means better protection against the type of corrosion caused by road salt, standing water and prolonged damp conditions.

For anything on the underside of the car, in the wheel arches or anywhere that sits wet for extended periods, the step up from A2 to A4 is worthwhile. The cost difference is smaller than you'd expect, especially when you measure it against how much longer the fixings will last and the labour needed to replace them if they corrode. For a kit car that might sit in a damp garage through the winter months, using A4 stainless steel fasteners is good insurance and well worth it for the peace of mind alone. 

Accu stocks A4 across nuts, hex nuts, cap heads, button heads, countersunk screws, hex bolts, nyloc nuts and washers.

High Tensile Steel (10.9 / 12.9 Grade) 

High tensile steel is essential for structural and high-load applications like chassis mounts, engine mounts and suspension pickup points. 

The grading system tells you exactly what you're getting: the first number represents the ultimate tensile strength divided by 100, so a 12.9 fastener has an ultimate tensile strength of approximately 1,200 MPa. The second number is the ratio of yield strength to ultimate tensile strength, giving a yield of roughly 1,080 MPa. That's 1.7 times the strength of an A2 stainless fastener, which is why high tensile is essential for structural joints where clamping force and fatigue life are critical.

The trade-off is that high tensile steel is not stainless. It's vulnerable to corrosion without protection, so while most 12.9 fasteners come with a black oxide or zinc plating, neither provides a long-term barrier in exposed or consistently wet locations. This is why high tensile is best reserved for structural applications where the joint is either shielded from direct moisture exposure or can be inspected and replaced at service intervals, rather than treated as a universal upgrade across the whole car.

It's also worth noting that higher-grade fasteners are more notch-sensitive, meaning they're less forgiving of surface damage or incorrect installation, which can weaken their tensile strength. It's another reason they belong on high-load joints where proper torque procedures are being followed. 

Accu's socket cap head screws are available in 12.9 grade and should always be paired with flat washers to protect finished surfaces.

Specialist Materials

The above three materials cover the vast majority of fasteners needed in any kit car build. But depending on the type of kit car you're building and your performance goals, there are some other material options for kit car components that are worth talking about too.

Titanium

For track-focused builds, hillclimb cars and any application where both weight reduction and tensile strength are the priority, titanium is worth serious consideration. It offers roughly 60% of the weight of steel at comparable or superior tensile strength to stainless, depending on the grade, and it’s naturally corrosion-resistant without any surface treatment. When used, it’s commonly found in suspension mounts, wishbone bolts, damper top mounts, brake caliper fixings and engine mounts.

The case for titanium at these joints is straightforward. Reducing unsprung mass (the weight of components not supported by the suspension) directly improves handling response, ride quality and tyre contact.

It’s not without downsides, with the most prominent being cost. Titanium fasteners are significantly more expensive than stainless steel equivalents, so most builds use them selectively by targeting the structural mounts where the strength-to-weight advantage is most valuable, rather than replacing fasteners wholesale across the car.

Accu stocks Grade 5 titanium screws in both socket cap and button head formats.

Aluminium

For purely weight-saving scenarios, aluminium is the lightest fastener option. However, its tensile strength is considerably lower than steel or titanium, so most kit car builds use them selectively on visible or high-count fixings like engine bay dress bolts and bodywork screws, rather than replacing every fastener on the car. Aluminium also sits relatively low in the galvanic series, so it's more anodic than both mild steel and stainless steel, meaning aluminium fasteners in contact with either in the presence of moisture will corrode preferentially and often quite aggressively.

It’s also used for non-structural, low-load applications such as interior trim screws, cosmetic covers and number plate fixings. Using aluminium fasteners in any load-bearing or safety-critical joint is not recommended.

Accu stocks aluminium socket cap head screws, as well as socket button flanged screws.

PEEK (Polyether Ether Ketone)

PEEK is a high-performance engineering thermoplastic with a very specific role on a kit car. It should never be used for structural or load-bearing joints as its tensile strength is a fraction of any metal fastener, but in some applications it outperforms metal entirely.

PEEK's standout characteristic is its combination of heat resistance, chemical resistance and electrical insulation. It handles continuous operating temperatures of up to 250 °C, which puts it comfortably within the thermal range of most underbonnet ambient conditions. It's important to distinguish between general engine bay temperatures and the heat produced by exhaust manifolds and turbochargers, whose surface temperatures can exceed 600 to 900 °C under load. PEEK is not suitable for fixings in direct contact with or in close proximity to exhaust or turbo components, metal fasteners remain the right choice there.

PEEK is resistant to brake fluid, coolant, engine oil, fuel and most solvents, all of which are present in a kit car engine bay and can degrade lesser polymers or attack plated metal surfaces over time.

Because PEEK is non-conductive, it's well-suited to sensor mounts, ECU brackets and any fixing where electrical isolation between the fastener and the component is important. This is particularly relevant on kit car builds where the wiring loom is custom-made and earthing paths need to be carefully controlled. A metal fastener in the wrong location can create an unintended earth path, leading to interference or erratic sensor behaviour. A PEEK fastener avoids that risk entirely.

The trade-off is cost and mechanical strength. PEEK's tensile strength is around 100 MPa, where A2 stainless steel’s is 700 MPa, so it's not suitable for anything structural. It's also significantly more expensive than nylon. But for the specific applications where heat resistance, chemical resistance and non-conductivity all matter at once, it's the right tool for the job.

Accu stocks PEEK screws in cap head, countersunk, grub and other head types, in thread sizes from M1.2 to M8.

Nylon

Nylon (polyamide) is the more accessible polymer option and covers a wider range of non-structural kit car applications than PEEK, at a fraction of the cost.

Its primary advantages are electrical insulation, chemical resistance and the complete elimination of galvanic corrosion. That last point is particularly relevant on a kit car with a mild steel chassis. Stainless steel fasteners in direct contact with mild steel can create a galvanic cell in the presence of moisture. One practical solution is to use nylon washers or nylon shoulder washers as insulators between the two metals, breaking the electrical contact that drives the corrosion process. Accu's nylon shoulder washers are designed for exactly this purpose.

Nylon fasteners are also non-marking, making them useful for mounting painted or polished panels where a metal fastener could scratch the surface during installation. This provides another layer of protection against galvanic corrosion beyond paint or a powder coating. For interior trim fixings, number plate mounts and non-structural cosmetic covers, nylon screws provide a lightweight, corrosion-proof fixing that won't damage the mating surface.

The limitation is temperature. Nylon's continuous operating range tops out at around 80 to 100 °C, which rules it out for anything close to the exhaust or engine block. For those underbonnet applications, PEEK is the better choice. Nylon is also significantly weaker than any metal fastener, so as with PEEK and aluminium, it should never be used in load-bearing or safety-critical joints.

Accu stocks nylon screws in thread sizes from M1.2 to M16, across cap head, countersunk, pan head and grub screw formats. Nylon hexagon nuts and nylon shoulder washers are also available.

A Note on Finishing and Aesthetics

Aesthetics play an important role in the design of your kit car, so are worth considering when it comes to fastener selection. While some like the contrast of silver components against dark coloured or black panelling, for others they’re an eyesore.

Accu offers a range of stainless steel components treated with a chemical conversion coating known as AccuBlack. This process isn’t a paint or a plating, so it doesn’t affect the dimensions or surface texture of the components themselves, but gives them a matte black finish by converting the top layer of the material into magnetite. Because it’s applied to a stainless steel fastener, you retain the full corrosion resistance of the base material beneath.

AccuBlack is available across a wide range of Accu's socket cap, button head and countersunk screw lines, making it a practical option for engine bay dress bolts, roll cage fixings, bonnet hardware and any exterior panel screw where a dark finish is preferred. For builds going for a stealth look, it can transform the overall appearance of the car without any compromise on performance.

Material Pairings and Galvanic Corrosion

Before finalising your fastener choices, it's worth understanding galvanic corrosion in a bit more depth. Kit car builds present more opportunities for it to occur than most people realise, and the area ratio effect in particular is worth knowing before you start specifying components.

In brief, galvanic corrosion occurs when two dissimilar metals are in direct contact in the presence of moisture. An electrochemical reaction takes place between them, with the less noble of the two corroding as a result.

This matters on kit car builds as there are a multitude of opportunities for it to occur. Stainless steel bolts bolted through a mild steel chassis are a prime example, in this case as the less noble of the two metals, the mild steel would corrode at an accelerated rate. It’s also worth noting that the corrosion is more pronounced when the surface ratio of the two metals is more skewed towards the nobler of the two. A small piece of mild steel in contact with a large piece of stainless steel would corrode much faster than a similarly sized or larger piece would.

There are several practical ways to avoid galvanic corrosion. Powder coating or painting the chassis breaks the contact between the two metals, though it’s important to remember to protect them during assembly, as any damage can remove that protection. A more reliable method is to ensure that, where metal pairings can’t be changed and direct metal-to-metal contact is unavoidable, nylon washers are used as insulators to prevent contact between the two metals and stop them from corroding.

A Note on Commodity Fasteners

Most kit car builders will already have a box of zinc-plated carbon steel fasteners to hand. While these are fine for general workshop use, they're not ideal as kit car parts. 

Commodity fasteners, which are mass-produced and made to minimum specification tolerances, often have inconsistent quality, uncertain grade markings and zinc plating that will degrade over time, particularly in exposed or underbody locations. There's also no traceability, so you can't be confident of the material grade or mechanical properties. 

For a vehicle that will need to be subjected to Individual Vehicle Approval (IVA) inspection to be used on public roads, sourcing fasteners from a specialist kit car parts supplier or a screw supplier like Accu with full traceability is a worthwhile investment in both safety and peace of mind.

Kit Car Fasteners by Build Area

The right fasteners for kit cars depend on what the purpose of the assembly is. For example, PEEK is a fantastic engineering polymer with exceptional underbonnet utility, but using PEEK fasteners to anchor the suspension would result in near-instant failure. What works perfectly in one application can be completely wrong for another, so rather than one 'best' fastener, there are right choices for each part of a kit car build.

We've broken things down by each area of the car to show which fasteners are the right fit for each job.

Chassis and Structural Fixings

Kit car chassis are predominantly tubular steel spaceframes. The fasteners holding them together need to handle sustained dynamic loads, road vibration and the occasional pothole impact. Hex bolts in high tensile steel are the natural choice here and M8, M10 and M12 sized bolts cover most chassis bracket and mounting plate applications. The external hex head allows high torque transfer with a standard spanner or socket, practical in tight spaces around a chassis rail when you can't get an L-shaped Allen key in at the right angle.

Where possible, pair them with flanged nyloc nuts rather than standard nyloc nuts. The integrated flange spreads the clamping load over a wider area, which is important on tubular chassis where a standard nut can bite into curved surfaces and create stress concentrations. The nylon insert provides some protection against vibration loosening, which is essential as a spaceframe kit car transmits more vibration to its fasteners than a monocoque road car ever will.

When bolting through mounting plates or brackets into chassis tubes, be careful about how much force you're applying. Over-tightening can deform thin-walled tubing, so don’t just wind them on as tight as possible. If the manufacturer's build manual specifies torque figures for chassis fixings, follow them. If it doesn't, refer to standard torque charts for the relevant bolt grade and diameter and err on the conservative side.

Remember to always use flat washers under bolt heads to distribute load and protect powder-coated or painted surfaces from marking during torque-up.

Body panels and GRP fixings

Fibreglass and composite panels present a different challenge: the material is brittle under point loads, so the fastener needs to spread its clamping force without crushing the laminate. Socket flanged button head screws are ideal here. The integrated flange acts as a built-in washer, distributing load across a wider footprint, while the low-profile domed head eliminates sharp edges that can snag or look untidy on exterior panels.

Over-tightening is a common issue with Glass Reinforced Plastic (GRP) panels. Unlike metal, fibreglass doesn't deform gradually under load. It resists, then cracks. If a panel feels like it needs more force to pull flat, the problem is usually from the fitting rather than the clamping force. Packing shims or re-trimming the panel edge is always a better solution than winding the fastener tighter.

For panels that need additional reinforcement behind the fixing point, bonded backing plates or penny washers on the reverse side spread the load across a much larger area of the laminate. This is worth doing on any panel that will see repeated removal and refitting, such as access panels or boot lids, where the mounting holes can deform over time.

For panels that won't need to be removed once fitted, blind rivets are worth considering. They're installed from one side only using a rivet gun, which is a significant practical advantage on a kit car where access behind a panel isn't always possible once it's in position. The mandrel is pulled during installation to deform the rivet body and lock the joint, creating a permanent fastening with strong shear resistance. Accu stocks blind dome rivets in A2 and A4 stainless steel as well as aluminium, with diameters from 2.4mm to 6.4mm. 

For GRP panels, peel blind rivets are particularly well suited as they're designed specifically for soft materials and thin panels. The peel action produced during installation spreads the clamping force across a wider area on the blind side, reducing the risk of pull-through. 

Where moisture ingress behind a panel is a concern, sealed blind rivets feature a locking mandrel that creates a watertight, vibration-proof seal. Finally, for panels where both a permanent fix and a flush exterior finish are needed, countersunk blind rivets sit flat against the panel surface.

Where a flush finish is needed, like in bonnet catches, boot hinges or any panel where a protruding head would spoil the lines, use countersunk screws or ultra-low socket cap heads where the panel is too thin for a countersunk recess. If the GRP hasn't been countersunk, Accu's solid countersunk washers convert a flat surface for countersunk screw use without any additional machining. 

Engine and drivetrain

The engine bay is where material choice and locking strategy matter most due to the combination of operating temperatures, chemical exposure and vibration affecting components. Socket cap head screws in A2 or A4 stainless are the standard for bracket mounting, ancillary fixings and anything visible under the bonnet. The cylindrical head and hex socket give a clean, purposeful look while allowing precise torque application.

Stainless steel is particularly well suited to engine bay use because it handles the combination of heat, moisture and chemical exposure far better than plated carbon steel. Coolant leaks, brake fluid splashes, oil mist and the general humidity of an enclosed engine bay all attack plated surfaces over time. With stainless, there's no coating to degrade.

For fixings where chemical exposure is the primary concern, PEEK fasteners are worth considering. Brake fluid, coolant, engine oil, fuel and most solvents are all present in a kit car engine bay and all of them can degrade lesser polymers or attack plated metal surfaces over time. PEEK handles continuous operating temperatures up to 250°C and is resistant to all of these chemicals, making it well suited to sensor mounts, fluid reservoir brackets and any underbonnet fixing where the fastener will be in regular contact with aggressive fluids, though as discussed earlier it should not be used in proximity to sources of extreme heat. Its non-conductivity makes it a practical choice for ECU and sensor fixings where electrical isolation matters, as covered in the material selection section.

Heat cycling, in addition to chemical exposure, presents a specific challenge. As an engine warms up and cools down through repeated use, the thermal expansion and contraction of surrounding components can progressively loosen threaded fixings. This is most pronounced on exhaust manifold brackets, alternator mounts, gearbox bell housing bolts and any fixing in direct contact with the block or exhaust system. 

Where heat cycling is the primary concern, belleville washers offer another line of defence. Unlike a flat washer, a belleville washer is cone-shaped and acts as a spring under the bolt head, flexing to maintain consistent clamping force as surrounding components expand and contract through thermal cycles. This makes them particularly useful on exhaust manifold brackets, turbo heat shields and any fixing where the temperature swing between cold start and full operating temperature is significant. How they work and how to stack them for different effects is covered in the anti-vibration section below. Accu stocks belleville washers in A2 stainless steel.

For engine and drivetrain applications, Accu's pre-applied threadlocking screws are worth considering. Rather than applying liquid threadlocker during assembly, the locking compound is factory-applied to the thread before dispatch. Like belleville washers, they’re covered in more detail in the anti-vibration section below.

Suspension and steering

These are the highest-stakes fixings on the car. Wishbone bolts, damper top mounts, steering rack clamps and anti-roll bar links all sit in the load path between tyre and chassis, so material grade matters.

The loads on suspension fixings are not static. A wishbone bolt doesn't just hold a set weight in place. It endures constant load cycling as the suspension compresses and extends over every bump, camber change and every time the brakes are applied. This dynamic loading generates fatigue stress, which over thousands of cycles can weaken a fastener that would have been perfectly adequate under a static load of the same magnitude. This is why 12.9 high tensile socket cap head screws or hex bolts are the right choice here. Their higher yield strength means they maintain clamping force under repeated loading and their fatigue resistance is substantially better than lower grades like 8.8.

On suspension joints, a fastener working loose isn't a cosmetic problem, it’s a potential catastrophe. This is why castellated nuts paired with split pins are the preferred locking method for safety-critical suspension and steering fixings. For wishbone bolts, ball joint retainers, steering linkage fasteners and any joint where failure could be catastrophic, use castellated nuts. Accu stocks full and thin castle nuts in A2 and A4 stainless steel, in sizes from M5 to M36.

Once suspension geometry is set, grub screws play an important role in locking adjustable components in position. Adjustable spring platforms, ride height collars, camber adjusters and clamping points on track rod adjusters all rely on a grub screw to hold the set position and prevent it from drifting due to vibration or load. Cup point grub screws are the best choice here as the concave tip bites into the mating surface and provides stronger resistance to movement than a flat point. For any grub screw in a suspension application, applying an AccuLock threadlocking patch is worth considering, as these fixings are small, subject to constant vibration and easy to overlook during routine checks. Accu stocks cup point grub screws from M1.6 to M20 in A2 and A4 stainless steel as well as high tensile steel.

Suspension, drive train and engine fixings should be torque-checked after the first 50–100 miles as components bed in and settle under load. A quick check with a torque wrench after the first few drives is straightforward and well worth the time.

Interior, trim and electrical

Inside the cockpit, safety and aesthetics take priority over raw clamping force. Button head screws in M4 or M5 are the go-to for dash rails, roll cage padding brackets and harness bar fixings. The smooth, rounded head won't snag or catch on a race suit.

This is more than just a matter of personal taste. If your kit car will go through the Individual Vehicle Approval (IVA) inspection in order to be legally driven on roads, the interior is assessed for projections that could cause injury in a collision. Sharp-edged fastener heads, exposed bolt threads and protruding hex heads can all result in a failure. Button head screws, with their low-profile domed surface and smooth radius, are one of the simplest ways to ensure interior fixings pass the projection test without needing additional coverings or caps. Alternatively, if they can be used practically, countersunk screws may also be an excellent choice for interior use, as their flush head has no protrusion.

For smaller electrical work like relay brackets, fuse box mounts and ECU cradles, M3 and M4 socket cap screws offer a more compact head profile and are easier to access with a ball-end hex key in tight cable looms.

Where electrical components are mounted to the bulkhead or transmission tunnel, consider using A4 stainless rather than A2. These areas are more exposed to engine bay heat and moisture migration, and the improved corrosion resistance of A4 provides a longer service life in locations that are difficult to inspect once trim panels are fitted.

Kit Car Parts by Build Area: At a Glance

The table below summarises the recommended fastener type, material and sizes for each build area to make component selection quicker and simpler:

Anti-vibration and Locking Strategies

Kit cars can be particularly susceptible to vibration-related issues, due to their tubular chassis designs, stiff suspension and a lack of any sound deadening. Left unchecked, vibration can gradually back a fastener out of its thread until clamping force is lost completely. 

Threadlocking compounds address this by either chemically bonding or mechanically locking the thread, preventing the loosening that sustained vibration causes. Accu’s pre-applied versions, where the compound is factory-applied to the screw before dispatch, offer more consistent coverage than liquid alternatives applied during assembly and save significant time when fitting dozens of fixings in a single build session. 

There are three pre-applied threadlocking compounds in the range, each suited to different applications. AccuLock is a low-strength, reusable microencapsulated adhesive, the right choice for general engine bay fixings and any joint you expect to revisit during servicing. Anu-Lok 180 is a nylon patch that creates a friction-based lock rather than a chemical bond, which means it isn't affected by oil, solvents or fuel contamination on the thread surface. It's rated to 120°C, making it well suited to fixings near the exhaust or block. Precote 80 is a high-strength, single-use adhesive for safety-critical fixings you don't intend to revisit, like suspension mounts, steering rack clamps, roll cage fixings and structural chassis joints where maximum resistance to loosening is the priority.

The table below summarises which compound suits each application:

Pre-applied compounds save time over liquid threadlocker and give more consistent coverage, useful when you're fitting dozens of fixings in a single build session.

Nyloc nuts

Where a threadlocking compound isn't practical, nyloc nuts are the standard alternative as they create a prevailing torque lock that resists vibration loosening. Flanged nyloc nuts add the benefit of a wider bearing surface, making them the better choice on tubular chassis, as covered in the chassis section above.

When it comes to kit car builds, nyloc nuts should be treated as single-use. The nylon insert retains the thread impression after removal and provides significantly less locking force on subsequent installations. For a kit car operating in a high-vibration environment, fitting new nyloc nuts whenever a joint is disassembled is straightforward and inexpensive insurance.

Castellated Nuts

For the most safety-critical joints on a kit car, neither threadlocking compounds nor nyloc nuts provide enough certainty. Both rely on friction or adhesion to resist loosening and both can be overcome by sustained vibration, heat cycling or dynamic loading. Instead, a more permanent mechanical solution is needed in the form of castellated nuts.

A castellated nut, also known as a castle nut, features a series of slots cut into the top of the nut like the crenellations on a castle battlement. Once torqued to the correct value, a split pin is passed through the nearest aligned slot and through a pre-drilled hole in the bolt shank. The pin physically prevents the nut from rotating in either direction. Unlike a friction lock it doesn't degrade over time and unlike an adhesive lock it can't be broken by heat or vibration. The only way to remove it is to pull the pin out.

This makes castellated nuts the preferred locking method wherever a loosened fastener could result in a catastrophic failure. As covered in the suspension and steering section, their primary home on a kit car is on wishbone bolts, ball joint retainers, steering linkage fasteners and any joint in the load path between tyre and chassis. Accu stocks full castle nuts and thin castle nuts in A2 and A4 stainless steel, in sizes from M5 to M36. Split pins are available separately to pair with them.

Rotational loosening and left-hand thread fasteners

Everything covered so far in this section deals with vibration loosening, where transverse vibration progressively walks the fastener loose. But there's another way fasteners can work themselves loose that’s worth understanding on a kit car where you may be fabricating custom linkages or working with rotating assemblies.

Rotational loosening occurs when a spinning component is actively pushing a fastener in the unscrewing direction. Unlike vibration loosening, which is gradual and cumulative, rotational loosening is driven by a sustained force in one direction. A standard right-hand thread tightens clockwise, so any component rotating counter-clockwise against that fastener is actively working to undo it. Threadlockers and nyloc nuts can resist this to a degree, but if the rotational force is continuous, the most reliable solution is to use a left-hand thread fastener. A left-hand thread tightens counter-clockwise, so the same rotational force that would loosen a standard fastener now acts in the tightening direction.

On a kit car, you're most likely to encounter left-hand threads in adjustable suspension and steering linkages. Track rod ends, adjustable tie rods and custom suspension links often use a turnbuckle-style arrangement where one end has a right-hand thread and the other a left-hand thread, allowing the effective length of the link to be adjusted by rotating the body without disconnecting either joint. Left-hand threads also come into play on custom-fabricated rotating assemblies where rotational force is transmitted directly to the fastener, such as pulley hubs or shaft retaining bolts on assemblies with a consistent direction of rotation.

A note on using anti-vibration washers

It's a common misconception that spring washers prevent vibration loosening. Despite the name, during proper assembly a spring washer flattens completely under clamping force and then functions in much the same way as a flat washer.

Spring washers do have a limited role. They provide some resistance to a fastener backing off under purely axial loading and a flattened washer can serve as a basic visual indicator that torque has been applied. On low-stakes fixings where the main concern is a fastener simply unwinding from a static joint, this may be sufficient, but on a kit car where real vibration is present they shouldn't be relied on as a locking device.

Belleville washers are a different matter entirely. Where a spring washer flattens and stops working under clamping force, a belleville washer is specifically designed to remain active. Its cone shape acts as a true spring under the bolt head, maintaining consistent preload even as the joint moves through thermal expansion, settling or minor relaxation. This is why they're recommended in the engine and drivetrain sections above for exhaust-adjacent and heat-cycled fixings, as they compensate for the dimensional changes that would otherwise cause a flat-washered joint to gradually lose clamping force. Belleville washers can also be stacked in two configurations for different effects: two washers facing the same direction, known as parallel stacking, create a stiffer preload, while two facing in opposite directions, known as series stacking, create a more flexible spring with greater travel.

If you're looking for a washer-based solution to maintain joint integrity on your kit car, belleville washers are the right tool. For vibration loosening specifically, nyloc nuts, castellated nuts and pre-applied threadlocking compounds remain the primary solutions.

Key Takeaways

Choosing the right fasteners for your kit car build comes down to three decisions at every joint: the right material, the right head type and the right locking strategy.

Material determines longevity and load capacity. A2 stainless steel covers the majority of fixings on a typical build, offering corrosion resistance through its full cross-section without any plating to degrade. Use A4 for anything exposed to road salt, standing water or prolonged damp. Reserve high tensile 12.9 grade for structural and suspension joints where clamping force and fatigue resistance are critical. Avoid using commodity fasteners with uncertain traceability on a vehicle that will be IVA inspected and driven on public roads.

Head type should match the application. Hex bolts for high-torque chassis work, socket flanged button heads for GRP panels, socket cap heads for engine bay and suspension, button heads for anything inside the cockpit where smooth, low-profile surfaces matter for both safety and IVA compliance.

Locking strategy matters more on a kit car than on a production vehicle. Tubular chassis, stiff suspension and minimal sound deadening create a harsh vibration environment. Flanged nyloc nuts, castellated nuts, pre-applied threadlocking compounds and proper torque procedures are the primary lines of defence against loosening. Most critical joints should use at least two of them.

With over 500,000 components available, no minimum order requirement and same-day dispatch, Accu make it straightforward to source exactly what your kit car build needs, whether that's three M4 button heads for a dash rail or a full suspension bolt kit in 12.9 high tensile. Every fastener ships with a certificate of conformity and Accu's engineering team is on hand to help if you're unsure which component is the right choice, making Accu the ideal choice of kit car parts suppliers for the UK and beyond.

Further Reading:

• What Does Strength Mean? - Understanding Material Properties in Engineering.

• What Causes Galvanic Corrosion And How Can I Prevent It?

• Stainless Steel: Types, Grades and Finishes.

• An Engineer’s Guide to the Best Screws for Confined Spaces.

• Pre-Applied Thread Lock: Types And Benefits.

• Why Top Formula Racing Teams Trust Accu for Motorsport Hardware.

FAQs

Q: Do I need high tensile bolts for my kit car?

A: High tensile fasteners are essential for structural and safety-critical joints, but they aren’t necessary across the entire build. 

Chassis mounting points, suspension pickup points, engine mounts and steering components all benefit from the higher clamping force and fatigue resistance of 12.9 grade steel. 

For body panels, interior trim and general engine bay bracketry, A2 or A4 stainless steel provides more than enough strength with the added benefit of corrosion resistance.

Q: Should I use threadlocker on kit car fasteners?

A: Threadlocker is a worthwhile addition on any fixing subject to sustained vibration or heat cycling, particularly in the engine bay and drivetrain. Pre-applied threadlocking compounds like AccuLock, Anu-Lok 180 and Precote 80 offer more consistent coverage than liquid alternatives applied during assembly and allow you to choose the right strength for the application. Low-strength compounds suit fixings you'll need to service, while high-strength options are better for critical fixings you don't intend to revisit.

Q: What size bolts do I need for a kit car chassis?

A: Most kit car chassis use M8, M10 and M12 hex bolts for structural fixings like bracket mounts and mounting plates. The specific sizes will depend on your chassis manufacturer's design and build manual.

Q: What fasteners pass the IVA interior projection test?

A: The IVA inspection assesses the interior for any projections that could cause injury in a collision. Button head screws are one of the simplest ways to meet this requirement, as their low-profile domed surface and smooth radius present no sharp edges. Where they can be used practically, countersunk screws are a good alternative, as their flush head sits level with or below the surface and presents no protrusion at all.

For many safety-critical systems, you also need component traceability. A full Certificate of Conformity is provided as standard through Accu, making them an ideal choice of kit car parts suppliers.

Q: Can I use stainless steel fasteners on a mild steel chassis?

A: Yes, but be aware of galvanic corrosion. When two different metals are in direct contact and moisture is present, an electrochemical reaction can accelerate corrosion of the more vulnerable metal, which in this case would be the mild steel chassis. In practice, the effect is usually minor provided the chassis has a good powder coat or paint finish acting as a barrier between the two metals. Where coating damage during assembly is unavoidable, nylon washers act as non-conductive insulators between the two metals, breaking the electrical contact that drives the reaction.