Allen Key (Hex Key) and Hex Bit Sizes Chart to show dimensions of
Allen keys (Hex keys) and bit sockets according to ASME B18.3-2003 standard.
Hexagonal (Hex) keys (Allen Keys) and bits sockets are tools which are used
to drive screws with a hexagonal socket. Hexagon Keys are furnished as Short
Arm Series or Long Arm Series.
Some important notes from the ASME B18.3:
- Hexagon keys and bits shall be fabricated from an alloy steel having two or more of the following
alloying elements: chromium, nickel, molybdenum, or vanadium, in sufficient quantity to ensure that the specified
minimum hardness of 48 HRC at the surface for nominal sizes up to and including 3⁄8 in., and 45 HRC for nominal sizes
over 3⁄8 in., is met when hexagon keys and bits are hardened by quenching from the austenitizing temperature and
Note1: For plated hexagon keys and bits, all dimensions are before plating.
Note2: For nominal socket sizes above 1 in., it is
recommended that bits be used in conjunction with standard hexagon wrenches or
power drives. Bits 1 in. and smaller are available,
but the lengths have not been standardized.
Note3: Length tolerance : +/- 0.062 inch
Designation: Product Name, Designation of the
Standard, Nominal Key or Bit Size, Series, Protective Finish (if required) Ex: ASME B18.3, 1⁄8 Short Arm Series
Wrench: A mechanical hand tool which is used to hold, twist, or turn an object (such as a bolt or nut).