spline shaft

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 mounted on a shaft might use a man spline on the shaft that fits the gear rack female spline on the apparatus. The splines on the pictured drive shaft match with the feminine splines in the center of the clutch plate, as the smooth suggestion of the axle is usually supported in the pilot bearing in the flywheel. An alternative solution to splines is a keyway and essential, though splines give a longer fatigue life.[2]