A spline distributes torque across several teeth around the shaft instead of concentrating the load in one key. It is useful when torque capacity, repeated assembly, accurate centring or controlled axial sliding makes a single parallel key unsuitable.
DIN ISO 14 covers straight-sided splines with internal centring. The principal identifiers are N number of splines, d minor diameter and D major diameter.
Shaft DIN ISO 14 · 6 × 23 × 26
This designation identifies six splines with d = 23 mm and D = 26 mm. The complete drawing must still state the relevant fit and manufacturing requirements.
Torque is transmitted through the working flanks of several spline teeth. The distributed contact can reduce local surface pressure and provide better concentric guidance than a single key.
Manufacturing variation, misalignment and elastic deformation prevent perfect equal load sharing. Capacity calculations therefore need the applicable standard method and a realistic load-distribution factor.
| Connection choice | When it fits the design |
|---|---|
| Parallel key | Simple, economical torque connection for moderate loads and straightforward machining. |
| Sliding spline fit | Torque transmission with intentional axial movement, such as a sliding coupling or gearbox member. |
| Transition spline fit | Accurate location with assembly still possible; control backlash and centring requirements. |
| Press spline fit | Fixed hub location where relative axial movement is not required and assembly force is acceptable. |