Pilot hole calculator

Self-tapping screws cut their own thread, so the hole under them has to be exactly right — too big and it spins, too small and the plastic cracks.

Screw diameter (mm)

Going into

Drill this hole

2.32 mm

Hard plastics need a fairly large hole or the boss splits.

Hole depth: about 1.5 to 2 times the screw diameter, so roughly 5.1 mm, plus a little clearance at the bottom for swarf.

Test on a scrap piece first

These are starting points. Plastic grades vary a lot, so drill one test hole, drive the screw, and if it feels like it might split, go up 0.1 mm.