Nissan Maxima 1998 A32 V6 Auto

[hodgins20]

does anybody know why on the original starter motor on my Maxima it has a spline length of 50mm but on the replacement I have had fitted the spline is only 30 mm long . I have now had flexplate / flywheel failure. the drive shaft is the same length but the original has a 50mm spline disappearing behind the scallop in the motor body but the replacement finishes well short of the scallop ???????????