How to Choose Brass Threaded Inserts for 3D Printing

If you've ever stripped a thread in a 3D-printed part, you already know why brass threaded inserts exist. They transform soft, weak plastic threads into strong, reusable metal ones — and once you start using them, you won't go back. This guide covers everything you need to know to choose and install the right insert for your project.

Why Use Brass Threaded Inserts?

3D-printed plastic (PLA, PETG, ABS, ASA) has poor thread strength. Tapping directly into plastic works for light, one-time assemblies — but repeated assembly and disassembly quickly strips the threads. Brass inserts solve this by providing a metal thread in a plastic body:

• 10–20× stronger pull-out force vs tapped plastic
• Fully reusable — assemble and disassemble hundreds of times
• Brass is soft enough not to damage the surrounding plastic during installation
• Works with all common FDM filaments

Types of Brass Inserts

There are two main types used in 3D printing:

• Heat-set inserts — installed with a soldering iron or dedicated heat-set tip. The heat softens the plastic, the insert is pressed in flush, and the plastic re-solidifies around the knurled outer surface. This is the most common and recommended type for FDM prints.
• Press-fit / ultrasonic inserts — pressed in cold or with ultrasonic vibration. Less common in hobbyist settings.

All inserts in our range are heat-set inserts suitable for standard soldering irons (recommended: 200–250°C tip temperature).

Choosing the Right Size

The insert size must match your screw size exactly. The most common sizes for 3D printing are:

Insert Size	Screw	Typical Use	Shop
M2	M2 screw	Miniature enclosures, small PCB mounts	M2 Brass Inserts
M2.5	M2.5 screw	Raspberry Pi mounting (standard Pi hole size)	M2.5 Brass Inserts
M3	M3 screw	3D printer frames, general maker projects	M3 Brass Inserts
M4	M4 screw	Heavier enclosures, structural joints	M4 Brass Inserts
M5 / M6	M5 / M6 screw	Large structural 3D prints, jigs	All Brass Inserts

Choosing the Right Length

Insert length determines pull-out strength. Longer inserts grip more plastic and resist higher loads. As a rule of thumb:

• Short inserts (3–4 mm) — light loads, thin walls, space-constrained designs
• Standard inserts (5–6 mm) — general purpose, most 3D printing applications
• Long inserts (8–10 mm) — high-load joints, structural assemblies, repeated disassembly

Your printed wall must be thick enough to accommodate the insert — leave at least 1.5 mm of plastic around the outside of the insert on all sides.

Designing the Hole in Your 3D Model

The hole diameter in your CAD model should be slightly smaller than the insert's outer diameter — the heat-set process expands the plastic to grip the knurling. Recommended hole diameters:

Insert Size	Recommended Hole Diameter
M2	3.2 mm
M2.5	3.5 mm
M3	4.2 mm
M4	5.4 mm
M5	6.4 mm
M6	7.4 mm

Note: Exact dimensions vary slightly by insert brand. Always check the datasheet for the specific insert you're using and test on a sample print before committing to a full run.

Installation Tips

• Set your soldering iron to 200–230°C — too hot and you'll melt surrounding plastic; too cold and the insert won't seat flush
• Apply gentle, even downward pressure — don't force it
• Use a flat surface or insert-alignment jig to keep the insert perpendicular
• Let the part cool for 30–60 seconds before applying any load
• If the insert pulls out during installation, the hole is too large — reprint with a smaller diameter

Which Filament Works Best?

• PETG — Excellent. Flows well around the insert, strong grip, low warping.
• ABS / ASA — Excellent. High heat tolerance means the insert seats cleanly.
• PLA — Good. Works well but has lower heat resistance — avoid high-temperature environments post-installation.
• TPU / Flexible — Not recommended. The material is too soft to hold the insert securely.

Summary

• Match insert size to your screw size (M2, M2.5, M3, M4, M5, M6)
• Choose length based on load requirements and wall thickness
• Design your hole ~1.2 mm smaller than the insert outer diameter
• Install with a soldering iron at 200–230°C with gentle pressure

Browse our full range: Brass Threaded Inserts — available in M2 through M6, in multiple lengths.