Heat-set threaded insert

Theory

Heat-set inserts use heat (200–240°C) to soften surrounding plastic so the knurled brass insert sinks flush and bonds mechanically. Sizes M2–M8 are common. Boss OD should be ≥2× insert OD to avoid splitting.

Application

Design a boss with hole diameter equal to the insert OD (no press interference: heat does the work). Boss OD ≥ insert OD × 2. Preheat tip to 200°C, set insert level on the hole, gentle downward pressure 5–10 s. Let cool 30 s before loading threads. Works in FDM (PLA, PETG, ABS), SLA post-cured parts, and SLS PA12.

Common mistakes

Do not overheat: melted plastic flows into threads and ruins the insert. Do not load perpendicular to the insert axis under impact. Very thin walls: use longer inserts to distribute load. SLS PA12: print hole −0.1 mm (porous sintered wall needs tighter fit).

Related terms: Printed threads / threaded joints, Press-fit joint, Clearance for moving / mating parts