Major diameter fit vs. side fit splines

Major diameter fit spline is suitable for applications where axes alignment between two parts (internal and external spline) is a critical design parameter. There are certain manufacturing challenges when dealing with major dia. fit splined couplings, mainly, the restrictions associated with the precision grinding of the internal spline's major diameter. In some cases this may not even be possible taking into the account the grinding wheel diameter and the amount of space required for the grinding head. Side fit splined couplings are widely used in all industries including automotive and aerospace. The main feature of this type of coupling is its self-centering ability under load. Although not as precise as the major diameter fit spline, this type of coupling serves successfully in a wide variety of applications. In some cases, to improve the axes alignment and reduce vibrations the spline pilot diameters are introduced.