Originally Posted by 90CvcDX
the way i was figured it was that both the hubs and tranny have to be swapped in order to use dx/si parts. for example say you have an si tranny and swap on some dx hubs it'll work as well as vice versa, now if you try std hubs with a dx/si tranny or dx/si hubs with a std tranny it wont fit properly, i own a 4spd std so i kinda would kno... i cant remember the exact numbers but i think std has like 4 or 5 less splines than dx and si have on their hubs and trannies.
EDIT: if you really wanna know just pull out one axle and compare it to your si counterpart.
all 88-91 L3 5 speed or 4 speed transmissions (except for the JDM ZC) will accept any model 88-91 CRX/Civic axle - the transmission end is the same on all of these axles - only the hub end is what is different - the Civic STD and CRX HF have smaller hubs and require different axles - STD 4 speed and HF 5speed use the same axle - DX, Si, LX and EX all use the same axle - unless you swap out the hubs, you just use whatever axle is made for your car and transmission model doesn't matter