125 Coupling Arm Question
 

I ordered a replacement coupling arm for my 125.
It attaches to the hydro shaft and the flexible coupling disc.
I used the cub cadet parts lookup to find the correct PN (759-3009 Arm, Coupling).
It seems that the replacement has a much bigger center where the shaft goes. The original fits snugly on the hydro shaft. What am I missing here? Or did I get the incorrect part shipped to me.

Looks like you looked up the correct part number.... are you saying the new part does not fit properly, as if not snug onto the pump shaft? Usually, a call to the supplier is what I'd do to rectify the issue.