Allen key in L-shape with a tip size of 1. A hex key is ideal for all types of use by every professional engineer, plumber, carpenter, electrician, but also for domestic use. Hex keys are formed from a single piece of hexagonal rod made of hard steel with blunt ends that fit comfortably into corresponding hex-shaped screw sockets. It is bent at 90 degrees, forming two arms of unequal length that resemble the Latin letter L.