What are Brass Threaded Inserts?

Brass threaded inserts, also known as heat set inserts or 3D print threaded inserts, are a core part of Accu's threaded inserts range, giving thermoplastic parts a hard-wearing metal thread that holds up to repeated assembly. Each one is a small, gold-coloured brass cylinder with a metric thread through its centre and an outer surface of diamond knurls, straight ribs, fins, slotted expansion legs or a self tapping thread, some with a thin flange at the top. Once that outer profile is locked into the plastic, the fastener's load passes into a metal thread rather than a moulded or printed one, so precision screws can be tightened and removed many times without stripping the part.

Brass inserts for plastic are used wherever a thermoplastic housing, bracket or cover has to come apart for access, adjustment or servicing. That makes them standard in consumer electronics enclosures, automotive trim and interior components, product development prototypes and 3D printed parts in PLA, PETG and ABS.

How Brass Threaded Inserts Work.

Most threaded brass inserts are fitted into a plain hole after the part is made. Heat set types are pressed in with a heated tip that softens the plastic around the insert, so it flows into the knurls and grips them as it cools; ultrasonic types work on the same principle, with vibration generating the heat, and Multisert inserts can be heat pressed, cold pressed or, in some versions, fitted ultrasonically. Press-in and expansion types go in cold, the expansion legs spreading outwards as the screw is driven, while self tapping types such as Thread-Fix and Trisert cut their own thread into the hole wall and moulded-in types such as Flow-Fix and Himould are placed in the tool before the plastic is injected around them. Whichever method is used, the outer profile resists both torque-out when the screw is tightened and pull-out when the joint is loaded.

Take a PETG gripper bracket printed for a desktop robot arm prototype and bolted to an aluminium servo horn with four M4 screws. During tuning those screws are loosened and retightened dozens of times, and printed threads would be worn smooth long before the design was finalised. With M4 heat set inserts pressed into the bracket, each screw bears on a brass thread instead, so the bracket can be repositioned as often as needed and the same inserts carry through into the production version. Once that bracket moves to injection moulding, Flow-Fix or Himould inserts can be moulded in during the shot rather than fitted as a separate operation.

Materials Brass Threaded Inserts Are Made From

Accu's brass inserts are manufactured from engineering brass, selected for how well it bonds with thermoplastics during installation:

• Brass: Conducts heat quickly and evenly, so a heat press or ultrasonic tool softens the surrounding plastic uniformly and the insert seats without scorching the part. It machines cleanly into fine knurls, ribs and threads, resists corrosion in most indoor and electronic environments and is supplied in a Natural finish, with the Multisert, Trisert and Himould inserts specifying CW614N free-cutting brass. Together, those properties make it the standard choice for threaded inserts for plastic.

Sizes & Types of Brass Threaded Inserts Available

The range is available in a variety of sizes and specific types to suit different thermoplastics, wall sections and installation methods:

• Internal Thread Size: M1.6 (1.6 mm) to M8 (8 mm).
• Length (L): 1.35 mm to 15 mm.
• Recommended Hole Size (HS): 2.3 mm to 10.6 mm.
• Minimum Wall Thickness: 1.3 mm to 6 mm.
• Flange?: Flanged and unflanged options.
• Insert Type: Heat-Fix, Tech-Fix, Sonic-Fix, Fin-Fix, Broach-Fix, Expansion-Fix, Thread-Fix, Flow-Fix, Multisert, Trisert and Himould.
• Installation Method: Heat Press, Heat Press / Ultrasonic Press, Cold Press / Heat Press, Cold Press / Heat Press / Ultrasonic Press, Press-In, Press-In Expansion, Self Tapping and During Moulding.

Not every insert type covers every size. M8 is available only as a Thread-Fix self tapping insert; the other ten types stop at M6. At the small end, M1.6 is a single flanged Multisert and M2.5 comes in Multisert, Trisert and Himould only, while M2 adds those three to the Heat-Fix, Sonic-Fix and Expansion-Fix designs. M3.5 is offered in Heat-Fix, Expansion-Fix, Broach-Fix and Thread-Fix. Flow-Fix and Himould inserts are moulded in during injection, so they have no recommended hole size (Himould lists its mould pin dimensions instead), and Minimum Wall Thickness is specified on the heat set and press-in Fix types only. Every brass insert in the range is specified for use with thermoplastics.

For wood, non-ferrous metal or threads above M8, Accu's Stainless Steel - (A2) self tapping inserts cut their own thread into a pilot hole and run up to M20, while Trisert-3 offers a self tapping alternative from M3 to M6 in stainless steel, titanium and zinc nickel plated steel; both sit in Accu's Threaded Screw Inserts range. As an alternative for plastic parts that will only be assembled once, Polyfix screws that thread directly into the plastic can remove the need for an insert.

FAQ

Q: What are brass inserts used for?

A: Brass inserts are used to give thermoplastic parts a strong, reusable metal thread, which stops screws stripping the plastic when a part is assembled and dismantled repeatedly. They are common in electronics enclosures, product development prototypes and 3D printed parts, where a component needs to be opened for access, adjustment or servicing.

Q: How do you install brass threaded inserts?

A: It depends on the installation method listed in each insert's tech spec. Heat set and ultrasonic inserts are pressed into a pilot hole with a heated or vibrating tip, press-in and expansion inserts are pushed in cold, self tapping inserts are screwed in so they cut their own thread and moulded-in inserts are placed in the tool before injection, while Multisert can be either cold or heat pressed. Accu's threaded insert installation guide walks through each method step by step.

Q: What size hole for brass inserts?

A: Each brass insert lists its Recommended Hole Size (HS) in the tech spec, ranging from 2.3 mm for the M1.6 Multisert up to 10.6 mm for the M8 Thread-Fix insert, with most Fix types held to a tolerance of -0/+0.1 mm. For example, the Heat-Fix M3 threaded insert needs a 4 mm hole with at least 1.8 mm of wall around it; for 3D printed parts, Accu's threaded insert hole size charts give tested dimensions for PLA, PETG and resin.

Bespoke Brass Threaded Inserts Manufacture.

High precision, bespoke manufacture of Brass Threaded Inserts to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.