Plastic threading.
Self-tapping.
Threading rules.
Plastic thread design — self-tapping, molded threads, threaded inserts. Each suits different applications. Design rules differ from metal threading.
Key principles.
Cheap
Threads molded directly. Cheap. Limited cycles.
Standard
Screw cuts thread in pre-drilled hole. Limited cycles.
Heavy duty
Brass insert pressed in, heated to fuse. 1000+ cycles.
Production
Ultrasonic vibration installs insert. Fast for production.
Plastic-friendly
Coarser pitches (vs metal threads) — less stripping risk.
Stronger
M5+ for plastic. Smaller threads strip easily.
FAQ
Self-tapping vs molded?
Self-tapping: handle higher loads, more cycles. Molded threads: cheaper, limited cycles. Choose per use.
Heat-set inserts?
Standard for quality plastic assembly. Strong, repeatable, 1000+ disassembly cycles.
Thread pitch for plastic?
Coarser pitches preferred — less stripping, easier engagement. Per ASME standards.
Boss design?
Boss diameter ≥ 2× thread diameter. Boss thickness ≥ 0.6× wall.
Pull-out strength?
Heat-set ~2000 N. Self-tapping ~1500 N. Material/depth dependent.
When does insert pay?
Repeated assembly, hot environment, structural load. Otherwise molded threads sufficient.
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