Splines are ridges or teeth[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 equipment mounted on a shaft might use a man spline on the shaft that fits the feminine spline on the gear. The splines on the pictured drive shaft match with the female splines in the center of the clutch plate, as the smooth tip of the axle is supported in the pilot bearing in the flywheel. An alternative solution to splines can be a keyway and important, though splines give a longer planetary gearbox fatigue life.[2]