Spline socket keys and bits dimensions chart according to ASME B18.3-2003 standard.

Spline socket keys and bits are tools which are used to drive screws with a spline socket . Spline Keys are furnished as Short Arm Series or Long Arm Series.

Some important notes from the ASME B18.3:

- Spline 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 0.372 in., and 45 HRC for nominal sizes over 0.372 in., is met when spline keys and bits are hardened by quenching from the austenitizing temperature and tempered.

Spline Socket Keys and Bits Dimensions:

Nominal key or bit and socket size


Dimensions of Spline Keys and Bits
Parameter Value
Nominal Key Size --- --- ---
Major Diameter [M] Mmax --- in
Mmin ---
Minor Diameter [W] Wmax ---
Wmin ---
Number of Spline --- ---
Width of Space [N] Nmax ---
Nmin ---
Length [B] Bmax ---
Bmin ---
Length [C]
(Short Series)
Cmax ---
Cmin ---
Length [C]
(Long Series)
Cmax ---
Cmin ---
Minimum Bend Radius Rmin ---
Maximum Chamfer Kmax ---

Note1: For plated spline keys and bits, all dimensions are before plating.

Note2: Bits are available, but lengths have not been standardized.


Designation: Product Name, Designation of the Standard, Nominal Key or Bit Size, Series, Protective Finish (if required) Ex: ASME B18.3, 0.111 Short Arm Series

Wrench: A mechanical hand tool which is used to hold, twist, or turn an object (such as a bolt or nut).


Link Usage
Spline Socket Dimensions Shows dimensions of a selected ASME(inch series) spline socket dimensions.
Socket Head Cap Screws Dimensions Shows dimensions of a selected ASME (inch series) hexagon and spline socket head cap screw.
Button Head Socket Cap Screws Dimensions Shows dimensions of a selected ASME (inch series) hexagon and spline socket button head cap screw.


  • ASME B18.3-2003, Socket Cap, Shoulder, Set Screws, Hex, and Spline Keys