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.
Browse self-tapping screw sizes →Gear for this job
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Self-tapping screws for plastic
Plastite / PT-style screws in an assorted box
Small drill bit set (0.5-3 mm)
Pilot holes under 3 mm need a proper micro bit set