Sometimes written as lock nuts, they also go by various other names, including half nuts, jam nuts and thin nuts.
Locknuts are used to lock a full nut in position to prevent it from working loose as a result of vibration or other factors.
Locknuts are often mixed up with Nyloc nuts, which are different. Nyloc nuts are self-locking nuts that feature a nylon collar in the top portion of the nut that locks the nut in place.
About UNF Left Hand Thread
UNF stands for Unified National Fine. It is a common imperial thread type with more threads per axial distance than its UNC equivalent.
Unified thread types (UNF and UNC) were introduced at the beginning of World War 2 to enable the interchangeability of machinery manufacturing between the USA, Canada and Great Britain. Still commonly found on a vast array of old machines and vehicles in the UK, UNF and UNC threads continue to be the standard thread in the USA and Canada.
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 a example the pedal of a bicycle on the left hand side.
