Self-Tapping Screw Boss
The window is narrow and it is easy to fall out of both sides. Hole too small and the boss splits from hoop stress as the thread forms; hole too large and the thread strips. Both source guides give the pilot hole as a fraction of the screw diameter and then insist you confirm it with trials — because the strip-to-drive ratio is what actually decides whether powered assembly works.
Torques must be measured, not calculated — both source documents say so explicitly, because the stripping torque depends on the resin, the moulding conditions and the exact screw geometry. A strip-to-drive ratio below about 5:1 leaves no room for tool scatter on a production line. Never re-use the same thread more than a few times: each insertion cuts or deforms material that is not coming back, and a metal insert is the right answer for anything assembled repeatedly.
Design guidance from manufacturer manuals, expressed as ratios to the nominal wall. Moulding outcomes depend on resin, tooling, gate location and process, so treat these as the starting point a moulder will refine. A helper, not a substitute for engineering judgment.