Which of the following washer types is not designed to prevent movement?

Flat washers are primarily used to distribute the load of a fastener, such as a bolt or a screw, over a larger area. This action helps prevent damage to the surface being fastened and can improve friction where the fastener contacts the material. However, flat washers do not have any specific design features that prevent movement or loosening of the fastener once it is installed.

In contrast, lock washers, shake-proof washers, and split-lock washers all incorporate designs intended to create a locking effect. Lock washers usually have a split or a bent design that provides tension and helps maintain the tightness of a connection, reducing the likelihood of loosening due to vibrations. Shake-proof washers are designed with features that grip the surface of the fastener and the material, further preventing movement. Split-lock washers also work by applying a spring action that helps maintain the clamp force.

Thus, flat washers lack these preventive features, making them the type that is not specifically designed to prevent movement.