spline shaft

Splines are ridges or the teeth[1][2][3] on a drive shaft that mesh with gear rack 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 female spline on the apparatus. The splines on the pictured drive shaft match with the female splines in the heart of the clutch plate, as the smooth tip of the axle is usually supported in the pilot bearing in the flywheel. An alternative to splines is usually a keyway and important, though splines give a longer fatigue life.[2]