The 2mm Allen key, which is also known as a hex key or Allen wrench, is a tool used for tightening or loosening screws or bolts with a hexagonal socket. It is a small L-shaped tool with a hexagonal tip that fits snugly into the socket of the screw or bolt. The 2mm size refers to the width of the hexagonal tip, which is used to fit into the matching socket size. The 2mm Allen key is used in a variety of applications.