A spline shaft is a torque transmission device that has either grooves or tongues machined along its length. The mating bearings run along either the groove or tongue, providing high rigidity. There are two main types of spline shafts: parallel key splines and involute splines. Parallel key splines have ridges with a square profile, while involute splines contain tapered ridges to decrease stress concentration. These items are used across a wide variety of industries, especially in transportation applications.

Selecting spline shafts

Teeth profiles of involute and parallel (square) spline shafts

Image credit: Pirate 4x4