The basic purpose of bolt and nut is to secure two material firmly together, and nearly everything made by man, using machinery or hand tools, uses nuts and bolts. However, when nuts and bolts become loose and fail at holding materials together. When that happens, it’s not a good thing, especially if the nuts and bolts are used to hold an auto mobile’s engine components together, or passenger seats. As you can imagine, nuts and bolts that vibrate loose can become a serious safety concern that is why preventing nuts and bolts from becoming loose is so important.

Because loose bolts are so common, we find one way to prevent: Washers.

Washers are typically wider than the bolt head, with the additional surface area adding extra friction to the joint to maintain the clamp force. However, simple split washers, sometimes called helical spring washers, have been found to actually loosen the bolt under vibration even faster than a joint with no washer. Conical, or Belleville washers, are cup-shaped washers that perform little better than spring washers in vibration tests.

Several types of locking washers have been developed, with flutings, ribs or teeth that dig into the surface of the joint during the tightening process, in order to prevent loosening. This may cause permanent damage to the joint finish or surface, which may be unacceptable, such as in critical aerospace applications where surface indentations may cause fatigue stresses. It may also prevent re-tightening of the joint to the proper tension.

Wedge-locking washers work in sets of two, with each washer having opposite facing wedges that interact with each other and with the joint and nut surfaces to prevent self-turning of the bolt. The wedges are designed to add tension (stretch) to the bolted joint if the bolt begins turning due to vibration or shock, preventing a loss of clamp force.