Splines having straight-sided teeth have been used in many applications (see SAE Parallel Side Splines for Soft Broached Holes in Fittings) however, the use of splines with teeth of involute profile has steadily increased since 1) involute spline couplings have greater torque-transmitting capacity than any other type 2) they can be produced by the same techniques and equipment as is used to cut gears and 3) they have a self-centering action under load even when there is backlash between mating members. Splined shafts are most generally used in three types of applications: 1 ) for coupling shafts when relatively heavy torques are to be transmitted without slippage 2) for transmitting power to slidably-mounted or permanently-fixed gears, pulleys, and other rotating members and 3) for attaching parts that may require removal for indexing or change in angular position. The latter construction weakens the shaft to a considerable degree because of the slots cut into it and consequently, reduces its torque-transmitting capacity. A splined shaft is one having a series of parallel keys formed integrally with the shaft and mating with corresponding grooves cut in a hub or fitting this arrangement is in contrast to a shaft having a series of keys or feathers fitted into slots cut into the shaft.

Ansi b92.1-1970 r1993