What is the purpose of using a lock washer with a fastener?

The use of a lock washer with a fastener primarily serves to prevent loosening. Lock washers are designed to maintain tension on the fastener by providing a form of resistance against vibrations and movements that could cause the fastener to become loose over time. By creating a mechanical grip, the lock washer helps secure the fastener in place, ensuring that it remains tightly fastened under operational conditions.

While increasing strength, providing insulation, or decreasing weight may be relevant in other contexts, those are not the roles of a lock washer. The essential function of this type of washer is specifically focused on maintaining the integrity of the joint by reducing the likelihood of unintentional loosening due to environmental factors, such as vibrations or thermal expansion and contraction.