gear rack 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 equipment mounted on a shaft might use a male spline on the shaft that matches the female 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 suggestion of the axle can be backed in the pilot bearing in the flywheel. An alternative to splines is usually a keyway and key, though splines give a longer fatigue life.[2]