Heat set inserts melt into a printed hole and leave a brass thread you can tighten again and again. Shop knurled inserts sold individually from M2 to M8, M3 and M5 packs of 100, a 120 piece starter kit and adapter tips for your soldering iron.
Brass Threaded Heat Inserts (Knurled) - Metric
M5 Heat Set Insert Pack (100 pcs)
M3 Heat Set Insert Pack (100 pcs)
Heat Set Insert Starter Kit (M2 to M5, 120 pcs)
A screw driven straight into plastic cuts its own thread, and that thread wears a little every time the part comes apart. Heat set inserts fix the problem. You press a knurled brass insert into a printed hole with a hot soldering iron, the plastic softens and flows into the knurling, and once it cools you are left with a metal thread locked into the part. Lids, access panels, fan mounts and printer upgrades can then be assembled and taken apart many times without stripping.
Our brass threaded inserts work with almost all FDM plastics, including PLA, PLA+, PETG, ABS and nylon, as well as most resins. For more project ideas, read Upgrade Your 3D Prints: The Power of Threaded Inserts.
Pick the thread size first, then the length. Short inserts suit lids, thin walls and shallow bosses where a longer insert would break through. Long inserts give more thread engagement in thicker sections that carry load. The M3 Thick is 5 mm wide and 4 mm long, matching designs such as Voron builds that call for an M3 x 5 x 4 insert.
| Product | What you get | Best for |
|---|---|---|
| Brass Threaded Heat Inserts (Knurled) - Metric | Sold individually: M2 Long, M2.5 Long, M3 Short, Long and Thick, M4 to M6 Short and Long, M8 Long, 1/4 Long | Exactly the sizes and quantities a project needs |
| Heat Set Insert Starter Kit (M2 to M5, 120 pcs) | 20 M2 Long, 20 M3 Short, 20 M3 Long, 10 M3 Thick, 15 each of M4 Short and Long, 10 each of M5 Short and Long | Designing with inserts for the first time |
| M3 Heat Set Insert Pack (100 pcs) | 50 M3 Short (3 mm long) and 50 M3 Long (5.7 mm long) | Printer mods, electronics enclosures and fan mounts |
| M5 Heat Set Insert Pack (100 pcs) | 50 M5 Short (6 mm long) and 50 M5 Long (9.5 mm long) | Aluminium extrusion frames and joints that take real load |
| Soldering Iron Adapter Kit for Plastic Heat Inserts | Brass adapter tips, metric M2 to M8 | Setting inserts straight with a standard soldering iron |
The hole is deliberately smaller than the outside of the insert, so the knurling has plastic to bite into. These figures come from our kit and pack listings. For M2.5, M6, M8 and 1/4 inserts, measure the insert and follow the size chart on the product page before you model the hole.
| Insert | Length | Insert diameter | Hole diameter |
|---|---|---|---|
| M2 Long | 3 mm | 3.5 mm | 3.1 mm |
| M3 Short | 3 mm | 4.5 mm | 4 mm |
| M3 Long | 5.7 mm | 4.6 mm | 4 mm |
| M3 Thick | 4 mm | 5 mm | 4.4 mm |
| M4 Short | 4 mm | 6 mm | 5.5 mm |
| M4 Long | 8.1 mm | 6.3 mm | 5.5 mm |
| M5 Short | 6 mm | 7 mm | 6.2 mm |
| M5 Long | 9.5 mm | 7 mm | 6.2 mm |
Printers, filaments and slicer settings all shift hole sizes a little, so print a test block at the listed diameter and set one insert before committing to a full part.
The iron, tip and a freshly set insert stay hot for a while, so use the iron stand and handle parts by the edges. Melting plastic gives off fumes, so work in a ventilated space, particularly with ABS, ASA and nylon.
Because the setting follows the printing temperature, each material needs a different heat. PLA and PLA+ take the lowest setting and soften quickly, so go slowly or the insert can sink too far and leave a raised ring. PETG runs hotter and likes to cling to the tip, so wipe the adapter clean between inserts. Nylon runs hotter again and grips the knurling firmly, but print it from dry filament so the walls around each hole are solid. Each filament's printing temperature is on its product page.
For more on bosses, walls and holes, see Designing for 3D Printing: DFM Basics.
Single inserts are sold individually, with an automatic 10% off when you buy 100 or more of a single size and 20% off at a quantity of 1,000 or more. If you are still working out which sizes you use, the starter kit is the easiest place to begin, while the M3 and M5 packs keep the busiest sizes on the bench. Orders ship from our Perth and Melbourne warehouses, with free shipping Australia-wide on orders over $299 (excluding PO Boxes).
The M3 Short and M3 Long inserts both use a 4 mm hole, and the wider M3 Thick uses a 4.4 mm hole. Model the hole at that size, then print a test piece and adjust slightly if the insert feels loose or pushes plastic up around the edge.
Use the printing temperature of the part's filament plus 10°C, so a PLA part gets a cooler iron than a PETG or nylon part. If the insert drops in with almost no pressure and plastic bulges around it, the iron is too hot. If you find yourself leaning on it, pause and let the heat soak through the brass.
An ordinary tip can set inserts, but a tip sized to the insert makes it far easier to get each one straight and flush. Our adapter kit covers metric M2 to M8 and suits most soldering irons. Check the ceramic sleeve measurements on the product page (24.8 mm deep, 3.85 mm inside diameter, 6.6 mm outside diameter) against your iron.
Standard metric machine screws of the same thread size, so an M3 insert takes an M3 screw. The M3 Fastener Starter Kit pairs neatly with our M3 inserts, and stainless screws in other sizes are on our nuts and bolts page. Choose a length that engages the full insert without bottoming out in the hole.
Usually the iron was too hot, or the insert was pushed rather than allowed to melt its way down. If an insert starts to tilt, stop while the plastic is still soft and bring it back to square with the tip. A slightly cooler iron, a slower press and a hole that is not oversized all help stop inserts sinking.
