Thread & Insert Reference

Look up recommended hole sizes for heat-set inserts and self-tapping screws in 3D printed parts by thread type.

How It Works

Heat-Set Inserts

Heat-set threaded inserts are small brass cylinders with external knurling and an internal thread. They are installed into 3D printed parts by pressing them in with a heated soldering iron tip.

• Hole diameter: Sized to be slightly smaller than the insert’s outer diameter (typically the knurl diameter minus 0.1–0.2 mm for standard inserts).
• Hole depth: Should be 0.5–1 mm deeper than the insert length to allow for any displaced plastic.
• Wall thickness: Maintain at least 2× the insert outer diameter of wall material around the hole for strength.
• Installation temperature: Set soldering iron to 200–220 °C for PLA, 240–260 °C for PETG/ABS.

Self-Tapping Screws

Self-tapping screws form their own threads as they are driven into a pilot hole. This is the simplest method but threads can strip if overtightened or reused many times.

• Pilot hole: Typically 75–85% of the screw’s outer thread diameter for FDM parts.
• Depth: Hole should be at least as deep as the screw engagement length, plus 1–2 mm clearance.
• Material matters: PLA and PETG hold threads well. ABS is acceptable. TPU is generally too flexible.
• Reuse: Threads weaken with each insertion cycle. For frequently disassembled parts, use heat-set inserts instead.

Clearance Holes

Clearance holes are sized so a bolt passes through without engaging. In 3D printed parts, holes print smaller than designed due to thermal shrinkage and the way circular paths are approximated by the nozzle.

• Close fit: Bolt passes through with minimal play. Good for alignment and precision.
• Free fit: Extra clearance for easy assembly. Recommended when precise alignment is not critical.
• FDM compensation: Values shown include extra 0.2–0.4 mm to compensate for typical FDM hole shrinkage.

Printer Calibration

Hole sizes vary between printers, materials, and slicer settings. The values in this reference are starting points for well-calibrated FDM printers. Always print a test piece first for critical applications and adjust hole sizes by ±0.1 mm as needed for your specific setup.