Fasteners

Not sure whether a printed part needs heat set inserts, thread forming screws or a nut trap? Our fasteners for 3D printing cover every method, from brass inserts and screws made for plastic to stainless nuts, bolts and ready-made kits.
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Choosing fasteners for 3D printing

Printed plastic is softer than metal and weaker along its layer lines, so how you join two parts matters as much as the hardware. There are four common methods: heat set inserts melt a brass thread into the part, thread forming screws form their own thread in a plain hole, captive nuts sit in a printed pocket called a nut trap, and through bolts clamp both parts between a head and a nut.

The best choice comes down to how often the part comes apart, how much load it carries and how much design work you want to do.

Fastening methods compared

Method and what to buyStrengthReusabilityDesign effort
Heat set inserts: Brass Threaded Heat Inserts (Knurled)High: a brass thread locked into the plasticMany assembly cyclesMedium: a sized hole and a soldering iron
Thread forming screws: SS304 Thread Forming Screws for PlasticsModerate: the thread is formed in plasticBest for parts assembled once or rarelyLow: a plain blind hole
Captive nuts: SS304 Standard Hex Nuts, Thin Hex Nuts or Galvanised Square NutsHigh: steel thread on steel threadMany assembly cyclesMedium: a hex pocket or square slot
Through bolts: Button Head Socket Screws with Nyloc Nuts and WashersVery high: both parts clamped between head and nutMany assembly cyclesLow: clearance holes, but you need access to both sides

Design tips for printed joints

Captive nut pockets

Model a hex pocket to the nut's width across the flats plus a little clearance: an M3 hex nut measures 5.4 mm across the flats and 2.3 mm thick. Thin hex nuts suit shallow pockets, and square nuts slide into a slot from the side of a part. To fully enclose a nut, pause the print just before the layer that closes over the pocket, drop the nut in and resume.

Hole sizes in general terms

Printed holes tend to come out slightly undersize, so give bolt clearance holes a little extra room over the thread diameter. Heat set inserts need a hole smaller than the insert, sized from the chart on our heat set inserts page. Our article on tolerances and fit explains how to dial holes in with test prints.

Thread forming screws need a pilot hole well under the thread size: about 1.8 mm for the 3 mm screws and 2.5 mm for the 4 mm screws, roughly 12 mm deep for 3 x 8, 15 mm for 4 x 10 and 22 mm for the 15 mm lengths. Add a small chamfer at the top of the hole for pan washer head screws.

Avoid over-tightening plastic

Too much clamping force can crack a printed boss or slowly crush the part, so tighten until snug and stop. Washers spread the load so heads and nuts do not pull into the plastic, and pan washer head screws have that washer face built in.

Fastener kits for getting started

Every kit also sits in our starter kits range.

Buying fasteners for 3D printing from OzFDM

Most screws, nuts, washers and inserts are sold individually, so a one-off repair only needs the handful of parts it uses. Single heat set inserts are automatically 10% off when you buy 100 or more of a single size and 20% off at a quantity of 1,000 or more. Orders over $299 ship free Australia-wide (excluding PO Boxes).

Fasteners for 3D printing FAQs

Should I use heat set inserts or thread forming screws?

Thread forming screws are the quicker option for parts you put together once, such as prototypes and fixed assemblies: model a plain hole and drive the screw in. For lids, panels and anything you open regularly, heat set inserts are worth the extra step, because the brass thread is stronger and survives repeated assembly without wearing.

Can I screw a normal machine screw straight into a printed hole?

It will often hold for the first assembly or two, but a machine screw is not made to form a thread in plastic, and the thread it leaves behind wears quickly. For a fast, permanent joint, use a thread forming screw designed for plastics. For a joint you will take apart, use a heat set insert or a captive nut instead.

Which fastener size is most common for 3D printed parts?

M3 is the size most printer parts and maker projects call for, so the M3 Fastener Starter Kit and M3 Heat Set Insert Pack make a sensible first order. M2 and M2.5 cover electronics and circuit boards, while M4 and M5 suit brackets, frames and aluminium extrusion builds where joints carry more load.

How do I stop printed joints loosening from vibration?

Use a nyloc nut, which has a nylon insert that resists loosening, or run a thin hex nut tight against a standard nut to lock it in place. Put washers under heads and nuts so the clamping force does not slowly sink into the plastic, and avoid simply adding torque, which can crack the part.

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