Roymech engineering encyclopedia

Straight-Sided Metric Spline Dimensions and Tolerances


Straight-sided splines provide a shaft-to-hub connection using multiple parallel-sided splines distributed around the circumference of the shaft. The mating internal spline engages these surfaces to transmit torque between the components.

Not sure which type of key or spline to use?
See the Key and Spline Selection Guide for an explanation of parallel, taper and Woodruff keys, straight-sided and involute splines, and when each type of shaft-to-hub connection is appropriate.

The dimensional data on this page is based on BS 5686:1986 and ISO 14:1982 for straight-sided metric splines with internal centring. The tables provide nominal dimensions for light and medium series splines together with recommended tolerances for sliding, close and fixed fits.

Reference data: Dimensions are in millimetres unless otherwise stated. For manufacture, inspection, procurement or contractual work, verify requirements against the applicable standard and engineering drawing.

Straight-Sided Spline Geometry

Straight-sided spline dimensions showing minor diameter outside diameter and spline width

The principal dimensions used to designate the spline are:

  • N – number of splines
  • d – minor diameter
  • D – outside or major diameter
  • B – spline width

The designation shown in the table takes the form N x d x D. For example, a designation of 6 x 23 x 26 identifies six splines with a 23 mm minor diameter and a 26 mm outside diameter.

Light and Medium Series Spline Dimensions

The following table gives the nominal dimensions for the light and medium series straight-sided splines.

d Light Series Medium Series
Designation N D B Designation N D B
mm     mm mm     mm mm
11         6 x 11 x 14 6 14 3
13         6 x 13 x 16 6 16 3,5
16         6 x 16 x 20 6 20 4
18         6 x 18 x 22 6 22 5
21         6 x 21 x 25 6 25 5
23 6 x 23 x 26 6 26 6 6 x 23 x 28 6 28 6
26 6 x 26 x 30 6 30 6 6 x 26 x 32 6 32 6
28 6 x 28 x 32 6 32 7 6 x 28 x 34 6 34 7
32 8 x 32 x 36 8 36 6 8 x 32 x 38 8 38 6
36 8 x 36 x 40 8 40 7 8 x 36 x 42 8 42 7
42 8 x 42 x 46 8 46 8 8 x 42 x 48 8 48 8
46 8 x 46 x 50 8 50 9 8 x 46 x 54 8 54 9
52 8 x 52 x 58 8 58 10 8 x 52 x 60 8 60 10
56 8 x 56 x 62 8 62 10 8 x 56 x 65 8 65 10
62 8 x 62 x 68 8 68 12 8 x 62 x 72 8 72 12
72 10 x 72 x 78 10 78 12 10 x 72 x 82 10 82 12
82 10 x 82 x 88 10 88 12 10 x 82 x 92 10 92 12
92 10 x 92 x 98 10 98 14 10 x 92 x 102 10 102 14
102 10 x 102 x 108 10 108 16 10 x 102 x 112 10 112 16
112 10 x 112 x 120 10 120 18 10 x 112 x 125 10 125 18

Straight-Sided Spline Fits and Tolerances

Straight-sided spline fit and tolerance dimensions

The standard provides tolerance combinations for sliding, close and fixed fits. The required fit should be selected from the functional requirements of the shaft-to-hub connection rather than by changing the nominal spline dimensions.

Tolerances on Hole Tolerances on Shaft Type of Fit
Not Treated After Broaching Treated After Broaching
B D d B D d B D d
H9 H10 H7 H11 H10 H7 d10 a11 f7 Sliding
f9 a11 g7 Close fit
h10 a11 h7 Fixed

Spline Symmetry Tolerances

The symmetry tolerance t controls the position of the spline width relative to the appropriate reference geometry. The values below vary with nominal spline width B.

Tolerance of Symmetry
Spline width B 3 3,5  4  5  6 7  8  9  10 12  14  16  18
Tolerance of Symmetry (t) 0,010 (IT7) 0,012 (IT7) 0,015 (IT7) 0,018 (IT7)

Using the Spline Tables

Start with the required standard spline designation and series. The nominal designation defines the number of splines and the principal diameters. The corresponding width B and tolerance combination then define the mating shaft and hub geometry.

The fit table distinguishes between sliding, close and fixed connections. A sliding fit permits relative axial movement of the mating components, while a fixed fit is intended for a connection that is not required to slide in service. The appropriate fit must be selected according to the functional requirements of the assembly.

These dimensional tables define standardized spline geometry and fits. They do not by themselves establish the torque capacity or service life of the connection.

Design Considerations

Compared with a single keyed connection, a spline provides multiple engaging surfaces around the shaft circumference. Actual load distribution between those surfaces depends on the geometry, manufacturing accuracy, alignment, fit and deformation of the mating components.

For a loaded spline connection, the designer should consider:

  • transmitted torque and any shock or reversing loads;
  • bearing pressure on the loaded spline faces;
  • shaft and hub strength;
  • required axial movement or axial retention;
  • fit and centring requirements;
  • manufacturing accuracy and spline symmetry;
  • wear and lubrication where relative movement occurs;
  • inspection and gauging requirements.

Key and spline strength calculations are provided separately on the Key and Spline Strength page.

Standard References

ISO 14:1982 – Straight-sided splines for cylindrical shafts with internal centering — Dimensions, tolerances and verification.

ISO 14 specifies straight-sided splines with internal centring and includes nominal dimensions, hole and shaft tolerances, symmetry tolerances and verification requirements.

ISO reviewed and confirmed ISO 14:1982 in 2026, and the standard therefore remains current.

BS 5686:1986 – Specification for straight-sided splines for cylindrical shafts: metric nominal dimensions, tolerances and gauging requirements.

Engineering use: RoyMech provides engineering reference data and guidance. Where spline dimensions or tolerances form part of manufacture, inspection, procurement, certification or a contractual requirement, consult the applicable standard and engineering drawing.

Related Key and Spline Information



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