KEVOS® MAKEOS · Power Transmission
S.A.E. Straight-Sided Spline Fitting (Width, Depth, Minor Diameter, Torque Capacity)
For an S.A.E. straight-sided spline fitting of 4, 6, 10 or 16 splines, what spline width, depth and minor diameter go with the nominal diameter and the fit I want, how much torque does it carry at the side pressure I allow, and is that enough for my torque?
Dimensions and torque capacity of an S.A.E. standard spline fitting (4, 6, 10 or 16 splines) by the handbook’s formulas for S.A.E. splines: spline width W (0.241D, 0.250D, 0.156D or 0.098D), and the depth h and minor diameter d for the permanent fit (A), sliding without load (B) or sliding under load (C), then the mean radius R = (D + d) ÷ 4 and the torque capacity T = p N R h per unit of bearing length (the handbook’s T = 1000 N R h at 1000 lbf/in² on the spline sides) for your side pressure and length, against the torque the fitting must carry.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal (major) diameter D | mm | Nominal major diameter of the spline fitting. |
| Number of splines | choice | Number of splines in the fitting. |
| Fit | choice | Permanent fit, sliding without load, or sliding under load. |
| Load | ||
| Bearing (engaged) length | mm | Length over which the hub and shaft splines bear on each other. |
| Side pressure allowed on the splines | MPa | Bearing pressure you allow on the sides of the splines; the handbook’s table capacities are for 1000 lbf/in² (6.895 MPa). |
| Torque to carry | N·m | Torque the fitting must transmit. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Nominal (major) diameter D
- What it is
- Nominal (major) diameter of the spline fitting.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Every dimension is a fixed fraction of it.
- Get it right
- The S.A.E. tables run from 3/4 to 6 in, depending on the number of splines.
What this means: Number of splines
- What it is
- Number of splines in the fitting: 4, 6, 10 or 16.
- Units and format
- Choose one of 4 options from the list: 4 splines; 6 splines; 10 splines; 16 splines.
- Example
- The form opens with “6 splines” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the spline width and the depth for each fit.
- Get it right
- More splines give a stronger fitting for the same diameter.
What this means: Fit
- What it is
- Fit of the hub on the shaft: permanent, sliding without load or sliding under load.
- Units and format
- Choose one of 3 options from the list: A: permanent fit; B: to slide without load; C: to slide under load.
- Example
- The form opens with “A: permanent fit” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sliding fits have deeper splines and a smaller minor diameter.
- Get it right
- There is no 4-spline fitting to slide under load.
Load
What this means: Bearing (engaged) length
- What it is
- Length over which the hub and shaft splines bear on each other.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The torque capacity rises in proportion.
- Get it right
- Use the length of the hub, less any chamfers.
What this means: Side pressure allowed on the splines
- What it is
- Bearing pressure you allow on the sides of the splines.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 10000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6.895 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The torque capacity rises in proportion.
- Get it right
- The handbook’s table capacities use 1000 lbf/in², which is 6.895 MPa.
What this means: Torque to carry
- What it is
- Torque the spline fitting must transmit.
- Units and format
- Enter a number in N·m: newton-metres. The form accepts 0.000001 N·m or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 N·m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the fitting when it exceeds the capacity.
- Get it right
- Use the peak running torque, including any shock.
Method and formulas
- W = 0.241D (4), 0.250D (6), 0.156D (10) or 0.098D (16).
- Fit A: h = 0.075D, d = 0.850D (4); 0.050D, 0.900D (6); 0.045D, 0.910D (10, 16).
- Fit B: h = 0.125D, d = 0.750D (4); 0.075D, 0.850D (6); 0.070D, 0.860D (10, 16).
- Fit C: h = 0.100D, d = 0.800D (6); 0.095D, 0.810D (10, 16); none for 4 splines.
- R = (D + d) ÷ 4; T = p N R h L (the handbook’s T = 1000 N R h lbf·in per inch at 1000 lbf/in²).
- Example: the fitting carries 16.101 N·m over 25.4 mm at 6.895 MPa on the spline sides.
Limitations
- The dimensions apply to soft broached holes; the handbook tables give the tolerances.
- The torque capacity assumes all splines bear evenly; spacing errors reduce it.
- Radii at the spline corners should not exceed 0.015 in (0.38 mm), and the splines should be parallel to the axis within 0.006 in per foot (0.5 mm per metre).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a straight-sided splined shaft and hole for a fit
- Check the torque capacity of an S.A.E. spline fitting
- Compare 4, 6, 10 and 16 spline fittings
Who it is for
- Machine designers
- Machinists
- Maintenance engineers
What you get
- Spline width
- Depth and minor diameter for the fit
- Mean radius of the spline sides
- Torque capacity per unit length and for the length
- Side pressure at your torque
Interpreting the result
- Take the side pressure from your design rules; the handbook’s tabulated capacities use 1000 lbf/in².
- A sliding fit has deeper splines and a smaller minor diameter than a permanent fit of the same size.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2279–2281. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · Library collection
Shafts, keys, couplings and alignment: connecting rotating machinery reliably
In Machine Elements and Mechanical Design
What it covers: Shafts crack at keyways and shoulders, couplings wear and misalignment quietly destroys bearings and seals. How to size shafts, join hubs, choose couplings and align machines properly.
Useful alongside · KEVOS® original book
Keyways, threads and splines
In Machine Part Repairs by the Numbers
What it covers: Repair worn keyways, threads and splines: check a key's shear and crushing stresses, choose between an oversize key, a new keyway and weld filling, and decide when a thread or spline can be restored.
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