Steel: 31CrV3 47-52 HRC Chromizing H: 60 mm Length: 190 mm The inch hex key (also known as an "allen key") is used for working with fasteners that have an internal hexagon. Angle keys have two levers in their design: an extended lever for maximum force application and a short lever for quick rotation. They are also used for working with fasteners in limited space conditions. High strength characteristics help prevent damage to the edges of the fastener.