Nyloc nut (nylon lock nut)

A nyloc nut is a self-locking nut with a nylon ring in its top. As the bolt threads cut into the nylon, friction holds the nut in place even under constant vibration, so no spring washer or thread locker is needed.

On motorcycles they are used on things like mudguard and bodywork fixings, brackets, footpeg mounts and some suspension bolts. Check the service manual: many critical fasteners, such as axle nuts and engine mounts, have their own specified type and torque.

The nylon loses grip each time the nut is used and is weakened by heat, so do not fit nylocs close to exhausts. Best practice is to replace a nyloc rather than reuse it, especially in safety-critical places.