Splines are ridges or tooth[1][2][3] on a drive shaft that mesh with grooves in a mating piece and transfer torque to this, maintaining the angular correspondence between them.

For instance, a gear mounted on a shaft might use a male spline on the shaft that fits the feminine spline on the apparatus. The splines on the pictured drive shaft match with the female splines in the heart of the clutch plate, as the smooth tip of the axle is usually backed in the pilot bearing in the planetary gearbox flywheel. An alternative solution to splines is a keyway and essential, though splines provide a longer fatigue life.[2]