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 gear gear rack mounted on a shaft might use a male spline on the shaft that fits the female spline on the apparatus. The splines on the pictured drive shaft match with the female splines in the heart of the clutch plate, while the smooth suggestion of the axle can be backed in the pilot bearing in the flywheel. An alternative to splines is certainly a keyway and important, though splines give a longer fatigue life.[2]