Steel: 31CrV3 47-52 HRC Chromizing H: 40 mm Length: 135 mm An angle hex key (also known as an Allen key) is used to work with fasteners that have an internal hexagon. Angle keys combine two levers in their design: a longer lever for applying maximum force and a shorter lever for quick rotation. They are also used for working with fasteners in confined spaces. The high strength characteristics prevent damage to the edges of the fastener. You can also buy a set of hex keys.