Lock Nuts — Nylon Insert, All-Metal, Jam & Castle Nuts

What are Lock Nuts?

A lock nut resists rotation once tightened. Prevailing torque types do this by friction: a polyamide insert (nylock) grips the bolt thread, or a deformed metal top section squeezes it. Jam nuts are thin nuts tightened against a full nut. Slotted and castle nuts are locked mechanically with a split pin through a drilled bolt. Lock nuts are used on rotating and vibrating equipment, pipe supports subject to vibration and fixings that cannot be retightened often.

Key features

• Nylon insert lock nuts to ISO 7040 (regular) and DIN 985 (thin)
• All-metal prevailing torque nuts to DIN 980 / ISO 7042 for higher temperatures
• Hex jam, heavy hex jam, slotted and castle nuts to ASME B18.2.2
• Carbon steel class 8 / 10 and stainless A2 / A4
• Zinc, hot-dip galvanised or plain finish

Specification

Applications

• Pumps, compressors and rotating equipment
• Vibrating pipe supports and skids
• Conveyor and material-handling equipment
• Electrical and instrument panels

Nylon insert vs all-metal lock nut

A nylon insert nut (ISO 7040 / DIN 985) locks by a polyamide ring that deforms around the bolt thread. It gives consistent locking but the insert limits service temperature, commonly to about 120 °C, and degrades with repeated reuse. An all-metal prevailing torque nut (DIN 980 / ISO 7042) locks by a deformed steel section, so it suits higher temperatures and solvent exposure, at the cost of higher installation torque.