Allen key

An Allen key, also known as a hex key, is a small tool used to tighten or loosen screws and bolts with a hexagonal (six-sided) socket in the head. It consists of a short arm and a longer arm, both forming a "L" shape, which fit into the hole of the fastener. Allen keys are common in furniture assembly, bicycles, and machinery, providing leverage and access in tight spaces. They are usually made of metal, and come in various sizes to match different screw heads for secure tightening.