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

For instance, a equipment mounted on a shaft might use a man spline on the shaft that matches 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, while the smooth tip of the axle can be supported in the pilot bearing spline shaftin the flywheel. An alternative to splines is usually a keyway and important, though splines provide a longer fatigue life.[2]