Lock Nuts - Metric Left Hand

A left hand thread is the terms used for a thread where the nut tightens in the opposite direction to normal. It is commonly used on items that rotate in a manner that could cause a normal right handed nut to loosen, for an example the pedal of a bicycle on the left hand side.

The most common thread type in production today. Usually specified as M then a number x another number. This signifies the thread diameter and the length of the fastener.

For example, M4 x 30 means that the major thread diameter (the external distance across the outside of the thread) is 4mm and the length is 30mm. Length is usually measured from the underside of the fastener head.