PT 4.0 / WN1412 4.0 self-tapping screws

Watch out for

• Radial stress can crack glass-filled nylon if hole is too small (~3.2mm typical)
• Torx T20 drive commonly required for 4.0mm sizes
• Phone, console, router, drone and vacuum teardowns almost always publish only driver type and length, not the thread-forming size. Fastener makers (EJOT Delta PT, Plastite/WN1412, Covestro plastics guides) publish sizes 1.6-10 mm with pilot-hole tables instead, so size the screw from the boss hole, not from a parts listing.