How to Install Self-Tapping Threaded Inserts in Metal, Plastic & Wood.

Fastening into softer materials like aluminium, brass, plastics, or wood often looks straightforward, but can often be deceptively complex. Traditional threads strip, fixings loosen and repeated assembly quickly degrades the surrounding material. What starts as a clean installation can turn into a reliability issue long before the product reaches the end of its service life.

Self-tapping threaded inserts are designed to solve this problem. By cutting or forming their own external thread into the host material, they create a durable internal thread capable of handling repeated assembly without wear. Used correctly, they provide strong, reusable fastening points in materials that would otherwise struggle to retain threads.

This guide explains how self-tapping threaded inserts work, how to prepare for installation and how to install them correctly in metal, plastics and wood. It also covers common mistakes and material-specific considerations, so the threads you install perform as intended.

Contents:

What Are Self-Tapping Threaded Inserts?

Choosing the Right Self-Tapping Insert.

Tools & Preparation.

How to Install Self-Tapping Threaded Inserts in Metal, Plastic & Wood.

Common Installation Mistakes

 

What Are Self-Tapping Threaded Inserts?

Self-tapping threaded inserts are cylindrical fasteners with an internal machine thread and a specially designed external self-cutting or forming thread. As the insert is driven into a pre-drilled hole, the external features cut or displace material to create a matching internal thread in the parent component.

Unlike press-fit or adhesive-bonded inserts, self-tapping designs rely on full mechanical engagement with the host material. This produces higher pull-out resistance, better protection against vibration and improved alignment between the insert and the fastener.

Self-tapping inserts provide a highly durable internal thread, making them an ideal solution for applications that require frequent assembly and disassembly without compromising the integrity of the parent material.

 

Choosing the Right Self-Tapping Insert.

All Self-Tapping Threaded inserts solve the same fundamental problem: creating a durable internal thread in a material that can’t reliably support one on its own. Where they differ is how they engage with the parent material during installation and how they behave once the insert is installed.

In practice, insert selection is rarely about thread size alone. It usually comes down to five practical considerations.

How the Parent Material Reacts During Installation.

Some materials cut cleanly, such as aluminium and brass, whereas others, like plastics, deform under pressure and heat. Materials like wood and MDF respond differently, as their performance depends on the interaction and compression of internal fibres rather than material flow or clean shearing. Self-Tapping Inserts perform best when their external thread geometry aligns with how the material deforms during installation.

How the Parent Material Resists Pull-Out.

Pull-out occurs when the axial load exceeds the parent material’s ability to resist the extraction of the insert. Inserts with longer thread engagement lengths and deeper external threads distribute load over more material surface area, improving pull-out resistance. In softer metals and plastics, shallow or short inserts often fail in pull-out-prone applications before the insert itself is stressed, damaging the surrounding parent material due to a lack of thread engagement.

How Self-Tapping Inserts Resist Spin-Out.

Spin-out happens when the insert cannot resist rotational torque and turns within the parent material after installation. This is strongly influenced by the external thread profile and flute design of your insert choice.
Inserts with sharper cutting edges or aggressive thread forms rely on clean installation to bite into the material; poor pilot hole sizing or smooth walls with a lack of engagement reduce rotational grip, particularly in plastics and wood.

How Material Creep Affects Self-Tapping Insert Performance.

In plastics, sustained load can cause the surrounding material to deform over time, reducing clamp force even if the insert initially feels secure after installation. Inserts with broader load-bearing thread geometry and sufficient external thread engagement length perform better here, as they reduce localised stress and slow material deformation.

Factoring, Splitting or Material Damage When Selecting Self-Tapping Threaded Inserts. 

In wood, MDF and brittle materials such as some plastics, failure often occurs during installation rather than in service. Inserts with overly aggressive threads or sharp cutting flutes can act like wedges, forcing fibres or layers in composites and plastics apart. Designs intended for fibrous materials use specialist, controlled thread forms to grip without inducing cracks, or plastic-specific inserts can use heat to avoid splitting.

Final Selection. 

In practice, insert selection is about understanding where and why a joint is most likely to fail, then selecting an insert whose external thread geometry works with the parent material rather than against it. Pull-out, spin-out, creep and material damage are not interchangeable risks; each points to a different balance of engagement length, thread form and cutting behaviour.

Focusing solely on insert strength or nominal pull-out values often leads to poor outcomes if the surrounding material cannot support the way the load is introduced. A joint that spins, creeps over time, or damages the parent material has already failed, regardless of how strong the insert itself may be.

If you’re unsure where to begin, start by matching the insert design to the parent material’s behaviour, then prioritise the failure mode you cannot accept. From there, refine the choice based on load, service life and how much control you have during installation. The following sections apply this approach to metal, plastics and wood in practical terms and outline example inserts you could use for each material.

Threaded Screw Inserts for Metal.

When Threaded Screw Inserts for Metal are the Right Choice.

Threaded screw inserts are well-suited to non-ferrous metals with lower shear strength than the fastener, most commonly aluminium, brass, bronze and some cast metals. In these metals, direct thread tapping often produces threads that wear quickly or fail under repeated assembly.

Self-tapping screw inserts for metal use cutting slots or flutes to form their own external thread during installation, creating a durable interface without pre-tapping.

How Threaded Screw Inserts for Metal Hold.

In soft metals, failure is rarely due to fastener strength alone. A self-tapping screw insert in metal improves performance by spreading thread engagement over a larger surface area than a tapped thread. This distributes the load into the parent material more evenly and also provides a stronger internal thread, especially when working with materials like brass and aluminium.

Key Buying Considerations for Self-Tapping Inserts For Metal:

Parent Material Hardness.

Pilot hole sizing directly affects cutting behaviour and must be matched to the hardness of the parent metal. Softer metals such as pure aluminium or brass tolerate tighter pilot holes for improved bite, while harder alloys like titanium or aluminium resist cutting more forcefully and require slightly larger pilot holes to control installation torque and avoid galling.
Where hardness is uncertain, a trial installation in scrap material is the most reliable way to confirm hole sizing.

Wall Thickness and Edge Distance.

Insufficient surrounding parent material reduces pull-out resistance and increases the risk of bulging or cracking during installation. As a general guide, the minimum wall thickness around the insert should be at least equal to the insert's outer thread diameter to support both radial installation forces and axial service loads.
Edge distance follows a similar principle; installing too close to a free edge concentrates stress and can result in deformation or fracture, particularly in thinner aluminium extrusions or cast housings.

Flanged vs Non-Flanged Inserts for Metal.

Flanged inserts spread surface load at the hole entry and provide a positive stop that limits over-driving during installation, which is particularly useful in softer metals where controlling depth by torque feel alone is less reliable. However, they require a flat seating face and add a small protrusion, which may not suit applications requiring a flush finish or minimal stack height. Non-flanged inserts allow flush or sub-surface installation but rely more on the installer to control seating depth accurately.

Metal Insert Materials and Corrosion Pairing.

Dissimilar metals in contact in the presence of moisture create conditions for galvanic corrosion, where the less noble metal corrodes preferentially. This is a particular concern when installing stainless steel inserts into aluminium, as the galvanic potential difference is significant, making corrosion in moisture-prone environments likely.
Brass inserts are generally a safer pairing with aluminium, though they offer lower mechanical strength. Where stainless steel must be used in aluminium, a barrier coating or sealant can help interrupt the electrolytic path. Insert material selection should account for the service environment early in the design process to help prevent these issues.

When to Avoid Threaded Screw Inserts for Metal.

Thin Sections With Limited External Thread Engagement.

Self-Tapping Threaded Inserts for metal need sufficient parent material for the external thread to bite and carry load. If the available material thickness is marginal, pull-out strength becomes unreliable and installation can distort or crack the surrounding material. In thin sheet metals or shallow bosses, the insert's external thread may only partially engage, meaning the few threads that do form carry a disproportionate share of the load.

If the parent material thickness doesn’t comfortably exceed the insert’s thread length, consider whether a Rivet Nut would be a more suitable alternative. 

Applications With Poor Control Over Installation Conditions.

Self-tapping inserts only perform consistently when pilot holes are correctly sized, the insert starts square to the surface and torque is applied in a controlled manner.
If access is restricted or torque control isn't practical, installation becomes unpredictable. This often leads to incomplete or misaligned thread formation, uneven engagement and lower spin-out resistance, particularly with cutting-flute designs that are less forgiving of angular error. In these situations, press-fit or adhesive-bonded inserts may offer more reliable results with less dependence on installer technique.

 

Threaded Screw Inserts for Plastics.

When Threaded Screw Inserts for Plastics are The Right Choice.

Self-tapping threaded inserts are a practical choice in plastics when a reusable machine thread is required with a higher strength than the parent material will support natively. Unlike heat-set inserts, which rely on softening the plastic so it flows around knurled features, self-tapping inserts for plastic achieve retention by cutting or displacing material under torque. This creates immediate mechanical engagement without the need for heat, ultrasonic equipment, or cooling time.

How Threaded Screw Inserts for Plastics Hold. 

In plastics, joint failure is rarely immediate. A self-tapping insert in plastic improves performance by spreading load across a broader thread contact area than a direct-tapped or modelled thread, reducing localised stress in the surrounding material. This provides more stable thread engagement over time, which is critical in plastics that creep and deform under sustained load.

Key Buying Considerations for Self-Tapping Threaded Inserts in Plastic.

Plastic Type.

Plastics respond very differently to cutting and displacement. Tough, ductile engineering plastics such as ABS, polycarbonate, Nylon (PA) and acetal (POM) can accommodate controlled cutting by the insert’s external threads, allowing clean engagement when pilot hole size and installation torque are managed correctly.

More brittle or filled plastics, including glass-fibre variants, are far less forgiving. These materials are more sensitive to aggressive thread forms and high insertion forces, increasing the risk of cracking or localised damage during installation. In these cases, insert geometries that spread load over a wider contact area and rely less on sharp cutting action, reduce stress concentration and improve installation reliability.

Wall Thickness and Edge Distance.

The surrounding geometry of the parent material does most of the holding work in plastics. Wall thickness and distance to free edges determine how much material is available to support the external thread. Thin walls or short bosses limit engagement and concentrate stress, making inserts in plastic far more sensitive to torque variation during installation. Generous wall thickness and consistent geometry in part design allow the insert’s thread form to distribute load rather than forcing the plastic to deform unevenly.

Installation control.

Self-tapping inserts in plastics rely on predictable installation conditions. Pilot hole accuracy, square starting and controlled torque determine how the external thread interacts with the material. Inserts with more aggressive cutting features are less tolerant of variation, while broader thread forms offer greater forgiveness when installation conditions aren’t perfectly controlled.

In plastics, insert selection is ultimately about choosing a geometry that works with material deformation, rather than fighting it. When stress is distributed cleanly and installation is controlled, self-tapping inserts provide reliable, serviceable threads in applications where plastics would otherwise struggle to retain them.

Threaded Screw Inserts for Wood

When Threaded Screw Inserts for Wood are The Right Choice.

Self-Tapping Threaded Inserts for Wood are used when bolts or machine screws are required in timber without degrading the wood fibres through repeated tightening. They’re common in furniture, fixtures, jigs, cabinetry and similar applications where joints need to be serviceable and maintain consistent performance over time. They’re particularly useful where direct fastening into the parent material would quickly loosen, strip, or damage the surrounding material.

How Threaded Screw Inserts for Wood Hold.

Unlike metals or plastics, wood does not support precise thread formation. Instead, wood inserts rely on mechanical fibre engagement. Coarse external threads and cutting features such as flutes displace and compress fibres as the insert is driven in, creating resistance to pull-out and rotation through friction and fibre interlock rather than material shear strength.

Performance depends on controlled wood fibre displacement during insert installation. Inserts that force fibres apart too aggressively can initiate splitting, while inserts with geometry matched to the material grip fibres without excessive damage, maintaining strength over repeated assembly cycles.

Threaded Screw Inserts for Wood Material and Size Constraints.

Accu’s Self-Tapping Wood Inserts are manufactured from zinc alloy and are available in M6 and M8 thread sizes, with both flanged and non-flanged options. Zinc alloy offers a great balance of strength and machinability for wood applications, while resisting the corrosion typically encountered in indoor furniture, fixture and cabinetry environments.

Insert diameter and engagement length have a direct impact on performance in wood. Larger diameter inserts engage more fibres around the circumference of the hole, improving rotational resistance, while longer inserts distribute axial load across a greater depth of material, reducing localised fibre crushing and improving pull-out resistance. This is particularly important in softer or lower-density timbers, where shorter inserts can fail to compress surrounding fibres under sustained load, leading to gradual loosening over time.

Hardwood vs Softwood vs Composites.

Hardwoods.

Dense hardwoods can accept more aggressive external thread geometries, but installation becomes more sensitive to pilot hole sizing and torque. Dense wood fibres resist displacement, so undersized holes or over-driving can quickly raise torque and cause splitting. Insert designs suitable for hardwoods aim to balance cutting action with controlled fibre compression.

Softwoods.

Softwoods are easier to install self-tapping inserts into, but their fibres crush more easily under load. This can reduce long-term grip if the insert's engagement length is too short. In these materials, longer inserts or flanged designs help spread load and improve stability over time.

MDF, Plywood and Particleboard.

Layered and composite wood materials behave differently from solid timber because their internal structure is less consistent. MDF is made from bonded wood fibres with no grain direction, giving it uniform properties but relatively low tensile strength, meaning it splits easily if installation forces are too high. Plywood offers more strength through its cross-laminated layers, but inserts that span a glue line between layers can encounter uneven resistance during installation, leading to inconsistent thread engagement. Particleboard is the least forgiving, as its loose, resin-bonded chip structure provides limited fibre interlock for the insert's external thread to grip.

In all three materials, performance depends heavily on clean drilling, accurate depth control and avoiding tear-out at the hole entrance. Pilot holes should be drilled at a moderate speed to reduce heat build-up and chipping. The pilot hole entry should be clean and free from tear-out. 
Over-driving is a common cause of weak installations. Once the insert passes its seated position, it compresses or fractures the surrounding material rather than improving retention in particleboard this damage is often irreversible. Flanged inserts can help limit over-driving and spread surface load across the weaker face material of composite boards, but still rely on correct installation for performance.

 

Key Buying Considerations for Self-Tapping Inserts in Wood.

Insert Length and Edge Distance.

In wood, performance depends heavily on how much material surrounds the insert. Adequate engagement length allows the external threads to distribute load across more fibres, reducing local crushing and improving resistance to pull-out over time. Inserts placed too close to edges concentrate stress in a small volume of material, creating crack initiation points that can propagate during installation or under load. 

Maintain a minimum distance of at least twice the insert's outer diameter between the centre of the hole and any free edge, and at least three times the outer diameter from end grain, where wood is significantly weaker and more prone to splitting.
These distances should be treated as starting points; softer timbers, composite boards and applications with higher service loads may require more generous margins to ensure correct performance.

Flanged vs Non-Flanged Designs.

Flanged inserts spread the load evenly at the pilot hole surface, reducing the risk of the insert sinking into softer faces or gradually chewing into the timber under clamp force. This is particularly beneficial in softwoods, MDF and laminated boards where surface fibres compress easily. Non-flanged inserts are better suited where a flush finish is required, but rely even more on correct pilot hole sizing and depth control to prevent over-driving.

Adhesive Use.

Adhesives are not required for most wood insert applications, but they can improve long-term stability in joints subject to vibration, cyclic loading, or high installation torque. Epoxy or wood glue helps bond the insert to surrounding fibres, reducing the likelihood of gradual loosening or rotation. Adhesive should be viewed as a stabilising aid rather than a substitute for correct sizing and installation. When utilising this solution, be sure you don't get any adhesive inside the insert as this would compromise the internal threads, rendering the insert unusable.

Tools & Preparation Before Installing.

Self-tapping Threaded Inserts rely on correct preparation to achieve their full performance. When installations fail, the cause is rarely the insert itself. The key problems outlined in this article, such as spin-out, pull-out, splitting, or damaged threads, almost always trace back to poor pilot hole quality, misalignment, or excessive installation torque.

Before installation, you should be able to control three things: pilot hole quality, alignment and how the insert is driven.

Essential Tools.

A Drill Capable Of Producing a Straight, Consistent hole.

The quality of the drilled pilot hole directly affects how the insert forms its external thread. A drill that can be held square to the surface and maintain a steady cut reduces the risk of angled holes, ovality or surface tear-out. 
Even small deviations in straightness increase insertion torque requirements and lead to uneven thread engagement, particularly with self-tapping designs that cut their own threads as they’re driven in.

• For metals such as aluminium and brass, use HSS (high-speed steel) or cobalt drill bits, which maintain a clean cutting edge in non-ferrous materials.
• For plastics, standard HSS bits work well, though a slower feed rate helps avoid heat build-up and material deformation.
• For wood, MDF and composite boards, a lip-and-spur (brad point) bit provides cleaner hole entry and better centring than standard twist drills, reducing tear-out at the surface.

The Correct Driver That Fits The Insert Fully and Securely.

The drive bit must fully engage the insert's drive feature without play. Accu's M6 and M8 wood inserts use a socket hex drive, requiring a 6mm or 8mm hex key, respectively. Poorly fitting tools or worn hex keys introduce play and cam-out risk, making it difficult to control insertion depth and increasing the risk of damaging the insert during installation. A secure fit ensures torque is applied smoothly and evenly as the insert cuts or displaces material.

Installing Inserts Without a Built-In Drive Feature.

Many self-tapping threaded inserts, particularly those designed for metal and plastic, feature only an internal thread with no integrated hex or torx drive. These inserts require a simple driving jig made from a bolt, nut and the appropriate hex key or torx driver to match the bolt head.

To assemble the jig: Partially thread a hexagon nut onto a bolt that both match the internal thread size of the threaded insert. 
Next, install this jig into the internal thread of the insert until the nut and top face meet as shown in our example.
This locks the insert to the bolt, allowing torque to be transferred from the bolt head through to the insert during installation. The insert is then driven into the pilot hole by turning the bolt using the appropriate hex key or torx key, depending on the bolt's head type.

Once the insert is correctly seated, hold the bolt stationary with your driver and loosen the nut to release it from the insert, then unthread the bolt. Take care during removal to avoid applying reverse torque to the insert itself, as this can loosen it in the parent material before it has fully settled.

This method gives consistent control over alignment and torque without requiring specialist tooling, and is one of the standard approaches for installing self-tapping inserts that lack a dedicated drive feature.

 

A Note on Cutting Slots.

Self-tapping threaded inserts without a built-in drive feature typically have a cutting slot at the base of the insert. This slot faces into the pilot hole during installation and serves two purposes: it allows the insert to cut cleanly into the parent material as it advances, and it deforms during installation to provide additional resistance to pull-out and rotation once seated.

A common mistake is to treat this slot as a drive feature for a flat-head screwdriver or bit. It isn't. Using it this way risks damaging the cutting geometry and compromising the insert's grip. Inserts without a dedicated drive feature should always be installed using the bolt-and-nut jig method described earlier in this guide.

Lubricant.

Lubrication reduces friction during installation, lowering the torque required for the insert to form its external thread. In metals like aluminium and brass, this helps prevent galling and improves thread quality. In dense hardwoods, lubricant reduces fibre tearing and limits the risk of splitting during insertion. Lubricant should be used sparingly; enough to stabilise cutting behaviour without contaminating the joint.

 

Pilot-Hole Quality.

The drilled pilot hole is the foundation of every installation. Its geometry determines how the insert cuts, how much torque is required and how evenly the load transfers into the surrounding material. A poor hole cannot be corrected by driving harder.

Drill the hole square to the surface so the insert enters on-axis. An angled hole forces one side of the insert to cut more aggressively than the other, increasing torque and producing uneven thread engagement. The hole entry should be clean and free from burrs, raised material, or torn fibres; any of these can cause the insert to start crooked, even if the hole itself is straight. Lightly deburring or breaking the edge before installation helps the insert seat correctly from the first turn.

Installation Control.

These principles apply equally whether you're working in metal, plastic, or wood.

Use slow, steady rotation so the insert can cut or displace material evenly. High speeds or impact drivers apply torque in spikes rather than smoothly, increasing the risk of thread damage, material crushing, or the insert biting unevenly. Hand tools or low-speed drivers give better feedback and control.

As the insert advances, resistance should build gradually and consistently. Sudden spikes in torque typically indicate an undersized hole, debris in the bore, or misalignment; forcing the insert past this point damages the newly formed threads rather than improving engagement. Drive the insert only until it sits flush with the surface, or just below it, depending on the design. Once seated, resistance rises sharply. This is the cue to stop. Continuing beyond this point compresses or tears the surrounding material and can distort the insert.

Where tolerances matter, perform a trial installation in scrap or off-cut material of the same type before committing to finished parts. This confirms pilot hole size, torque feel and seating depth, and reduces the risk of rework.

 

How to Install Self-Tapping Threaded Inserts In Metal, Plastic and Wood. 

The preparation principles covered above apply to installing self-tapping threaded inserts regardless of the parent material. What changes between metals, plastics and wood is how the parent material responds as the insert cuts its way in. The following sections break down the specific installation steps and considerations for each material type.

How to Install Threaded Inserts in Metal.  

Aluminium and brass are the most common substrates for self-tapping threaded inserts in metal. Both cut cleanly and respond well to controlled installation, but metals have specific requirements around lubrication and torque that affect thread quality and long-term performance.

Step-by-step installation:

 

Drill the pilot hole.

Utilising the correct HSS drill bit, drill the hole to the diameter specified for the insert size and material.

Check you have the right size with our Insert Pilot Hole reference tables. Keep the drill square to the surface; even slight angular error will cause uneven cutting as the insert enters, increasing torque and reducing thread quality on one side of the hole.

Where possible, use a rigid setup (pillar drill or guide) rather than freehand drilling for more consistent results.

 

 

 

 

 

Deburr and clean the pilot hole.

Lightly deburr the hole entry and remove all swarf. A clean, well-defined edge helps the insert start on-axis from the first turn. Burrs or trapped chips increase resistance during installation and can cause the insert to tilt or bind early, even if the hole itself is correctly sized.

Apply lubricant.

Apply a light lubricant to the insert or the hole. This is particularly important in aluminium, where lubrication reduces friction and galling at the cutting edges. Lower friction allows the insert to cut rather than smear material, producing cleaner threads and more predictable installation torque.

 

 

 

 

 

 

Drive the insert.

Using your driving jig mentioned earlier and the correctly sized drive bit, turn the insert in at a slow, steady speed. The goal is controlled cutting, not rapid insertion. Avoid impact drivers or high rotational speeds, as these reduce feedback and make it easier to over-torque or cross-start the insert before the thread has properly formed.

 

 

 

 

 

Seat the insert.

Continue driving until the insert sits flush with the surface, then stop. Once seated, additional torque does not improve retention and often deforms the insert or damages the newly formed threads in the parent material. A correctly installed insert should feel stable without needing to be forced home.

Material-specific notes.

• Aluminium: Lubrication is strongly recommended. A light machine oil or suitable cutting fluid reduces galling, improves surface finish and lowers installation torque.

• Brass: Lubrication is generally not required. Brass cuts cleanly and has good natural lubricity; instead, use lower torque and steady rotation to avoid deformation.

 

Installing Self-Tapping Threaded Inserts in Plastics.

The core installation principles, pilot hole quality, square alignment and controlled torque, apply to plastics just as they do to metals and wood. However, plastics are less forgiving of variation. Pilot hole sizing is critical: too small and the material risks splitting; too large and thread engagement drops significantly. Torque sensitivity is also higher, as most thermoplastics deform rather than shear under excess force.

Because plastic behaviour varies widely between material types, from ductile engineering grades like ABS and nylon to more brittle filled compounds, installation guidance needs to be tailored accordingly. For full step-by-step instructions covering material selection, pilot hole sizing and installation technique, refer to our dedicated guide.

Threaded Inserts & Fasteners for Plastic
 Installation Guide.

 

How to Install a Threaded Insert in Wood.

Threaded inserts for wood allow machine screws and bolts to be used reliably in timber, creating serviceable joints in furniture, fixtures, jigs and structural assemblies. Unlike metals or plastics, wood relies on controlled fibre engagement rather than cutting a clean, continuous thread, so pilot hole preparation and alignment have a direct impact on strength and longevity.

The aim during installation is to engage fibres evenly without crushing or splitting the surrounding material, allowing for maximum thread/flute grip.

Step-by-Step Installation:

Drill the pilot hole.

Using the correctly sized lip-and-spur drill bit, drill a pilot hole typically 0.5 - 1.0 mm smaller than the insert’s outer diameter, unless otherwise specified. The hole size controls how aggressively the insert engages the fibres; too small and the wood may split; too large and pull-out resistance drops.

For the correct pilot hole sizing for your insert, see our pilot-hole reference tables.

 

 

 

 

 

Prepare the hole.

Ensure the pilot hole is straight, clean and free from fibre tear-out. A skewed or ragged hole causes uneven fibre loading as the insert is driven, increasing installation torque and reducing long-term holding strength. Clearing chips and loose fibres allows the insert to seat cleanly rather than compacting debris.

 

 

 

 

 

Start the insert square.

Position the insert carefully and begin threading it in by hand, utilising the appropriate socket hex bit. Starting square to the surface is critical; once the insert begins cutting into the fibres, alignment cannot be corrected without weakening the surrounding wood.

Drive the insert steadily.

Once you have confirmed the starting position is square, continue driving the insert into the parent material. The insert should advance smoothly with consistent resistance. Sudden increases in torque often indicate misalignment or an undersized hole.

 

 

Seat the insert.

Continue driving until the insert sits flush with the surface, or slightly below it for non-flanged designs. Once seated, stop. Driving further offers no benefit and can crush fibres around the insert, reducing pull-out resistance. 

Tips for best results.

• In dense hardwoods such as oak, maple or beech, a light application of wax or dry lubricant to the insert or pilot hole can reduce installation torque and limit the risk of splitting. Lubrication helps the insert advance through tightly packed fibres without forcing them apart, particularly in installations close to edges or end grain. In softer timbers, MDF and particleboard, lubrication is generally unnecessary; the fibres offer less resistance during installation and the insert needs that friction to grip effectively.

• In high-load or vibration-prone joints, a small amount of epoxy or wood glue can be used to stabilise the insert after installation. Adhesive isn’t required for most applications, but it can help limit long-term loosening in softer timbers, MDF, or particleboard by bonding loose fibres and reducing micro-movement around the insert under cyclic load.
  
  

Common Self-Tapping Insert Installation Mistakes.

Using self-tapping inserts in hardened or ferrous metals.

Self-tapping threaded inserts are designed to cut or form threads in softer substrates. When used in hardened or ferrous metals such as steel or stainless steel, the parent material resists cutting, causing installation torque to rise sharply. This often results in damaged cutting flutes, distorted inserts, or seizure part-way through installation. Even if the insert appears to install successfully, thread engagement is usually inconsistent and long-term reliability is poor due to galling and dissimilar metal interaction. In these material types, the recommended solution is to directly tap the thread and use the correctly sized fastener.

Incorrect pilot hole size or depth.

Pilot hole dimensions directly control how the insert engages the surrounding material. A hole that is too small increases installation torque and stresses the parent material, leading to splitting, distortion or thread damage. A hole that is too large reduces external thread engagement, lowering pull-out strength and increasing the risk of spin-out under load. Insufficient hole depth can also prevent full seating, causing the insert to bottom out before proper engagement is achieved.

Installing without lubrication in aluminium.

Aluminium is prone to galling when metal surfaces slide against each other under load. Installing a self-tapping insert dry increases friction at the cutting edges, causing material to smear rather than shear cleanly. This raises installation torque, increases the risk of the insert binding during installation and produces rough, uneven threads that compromise strength and consistency even if the insert seats flush.

Applying excessive torque during installation.

Driving the insert with excessive torque does not improve retention. Instead, it deforms the insert or damages the newly formed external threads in the parent material. In softer materials, this often leads to localised substrate collapse that isn’t immediately visible but reduces pull-out resistance and causes inconsistent fastener behaviour during later assembly. Excess torque also increases the likelihood of seizure during installation.

Misalignment during starting, leading to angled threads.

If an insert is started at an angle, the external thread cuts unevenly, with one side carrying more load than the other. This increases installation torque, weakens engagement on the unloaded side and leaves the insert mechanically compromised even if it appears flush at the surface. Misalignment is a common cause of early spin-out or loosening under service loads and cannot be corrected once the insert has begun cutting.

Wrapping Up.

Self-tapping threaded inserts are a practical solution to a common fastening problem, but they rely on correct selection and installation to perform as intended. When the insert matches the material and the pilot hole is prepared properly, the result is a durable, repeatable thread that outperforms direct fastening in softer substrates.

Whether you’re reinforcing aluminium housings, adding serviceable threads to plastics, or upgrading timber joints, a methodical approach pays off. Take the time to prepare the pilot hole, control installation torque and choose the right insert for the material so the threads you install will last.

Further Reading: 

How To Use And Read A Micrometer - Discover the science of metrology and how to measure in Microns with Accu. 

Ultimate Screw Buying Guide - The Complete Guide to Threaded Component Selection At Accu. 

The Engineering Careers A-Z List 2026 - Discover New Career Options & Ideas With Detailed Salaries for 2026.

 

FAQs

Q: How are threaded inserts installed?

A: Drill a pilot hole, position the insert and drive it in using the correct tool at controlled torque. Ensure perpendicular alignment and use adhesives or lubricants if specified.

Q: Should I glue in threaded inserts?

A: Not always. In wood and some plastics, adhesives like epoxy or Loctite improve grip. In metals, mechanical friction usually provides sufficient retention.

Q: How to drill a hole for a threaded insert?

A: Use the pilot hole size recommended by the manufacturer;  typically just below the insert’s minor thread diameter. Maintain clean edges and accurate depth.

Q: What size drill bit do I need for threaded inserts?

A: It depends on the insert’s thread size and material. Check the product data sheet on the relevant Accu product page for precise recommendations.