Locking devices for screwed fastenings

Locking devices for screwed fastenings

Locking devices are employed to prevent threaded fastenings from slacking off in use as a result of vibration. they are divided into two categories. Those which depend upon friction and those where the locking action is positive. Positive locking devices are more time consuming to fit, so they are used only for critical joints where failure could cause serious accidents, for example the control systems of vehicles and aircraft

1- Friction locking devices
Frictional locking devices are devices that perform the above functions using the coefficient of friction between the two contacting surfaces

Lock nut

Stiff nut (insert)

Stiff nut (slit head)

Serrated lock washers

Single coil square section spring washers: metric series, type A

Double coil rectangular section spring washers: metric series, type D

Toothed lock washers

Type V countersunk

2- Positive locking devices

A positive locking device is a device used in conjunction with a fastener in order to positively lock the fastener. This means that the fastener cannot work loose from vibrations.

Slotted nut