Spring Washers

Spring Washers:

Spring washers, which have axial flexibility and are used to prevent fastening or loosening due to vibrations.

Locking washers, which prevent fastening or loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers.

What is the difference between a flat washer and a spring washer?

Plain and spring washers are both used to distribute the load of a fastener. The difference lies in their shape. Plain washers are flat, whereas spring washers are curved.