What is the function of a cotter pin in fastening?

A cotter pin serves as a fastening device that secures components together by locking them in place. Typically made from a flexible material, the cotter pin is inserted through a hole in a fastener (like a bolt or a clevis), and its tails are bent back to prevent it from slipping out. This mechanism ensures that parts remain securely connected under various conditions, which is crucial in military operations where reliability of equipment is paramount.

The other options pertain to different functions not associated with cotter pins. Adjusting tension generally involves other types of hardware or mechanisms rather than a cotter pin. Providing electrical connectivity relates to connectors or wires, and facilitating movement would mean components can move freely, which contradicts the purpose of securing with a cotter pin. The primary role of a cotter pin is indeed to keep assemblies intact and secure, making the correct choice clear.