Plastic Screw Torque & Installation Guide
Plastic Screw Torque & Installation Guide
Plastic screw installation differs fundamentally from metal. Plastics have low modulus and high thermal expansion; improper torque causes stripping, breakage or stress cracking.
1. Recommended Torque (Reference)
- M3 PA66: ~0.3-0.5 N·m
- M4 PA66: ~0.8-1.2 N·m
- M5 PA66: ~1.5-2.0 N·m
- M3 PEEK: ~0.4-0.6 N·m
- M5 PEEK: ~2.0-2.5 N·m
Values depend on material, thread size and mating material. Actual testing recommended.
2. Avoiding Stripping
- Use torque-limited drivers
- Prefer machine screws with tapped metal inserts
- Ensure proper thread hole tolerance
- Clean threads before assembly
3. Avoiding Stress Cracking
- Avoid excessive tightening force
- Allow thermal expansion clearance at high temperature
- Mind humidity effects on hygroscopic materials like PA66
- Use spring washers or flange nuts for critical applications
4. Temperature Effects
Plastic strength decreases at high temperature; reduce torque accordingly. PA66 at 80°C: ~60% of room-temperature torque.
Conclusion
Proper torque control is key to reliable plastic fastening. FASTKING provides torque reference tables and installation advice.