Which of the following is an example of a locking device?

• A. Lockwire or keeper
• B. Pressure relief valve
• C. Safety pin
• D. Fuse block

Answer: (A)

A locking device is something used to keep parts from loosening or moving apart during operation, especially under vibration or dynamic loads. Lockwire works by threading through holes in two parts and twisting the wire so the assembly cannot rotate or back off; that physical tie keeps fasteners secure. A keeper plays a similar role as a retainer that holds components in place and prevents unintended movement. Together, they’re specifically designed to prevent loosening and unintentional disengagement.

The other items do not serve that purpose: a pressure relief valve is a safety device that vents excess pressure rather than locking components; a safety pin is a temporary fastener used to hold parts together temporarily and can be removed easily; a fuse block is for protecting electrical circuits, not securing assemblies.