Balance Shoe

Looking for balance shoes. These are the balance shoes out of our Manchester Single Hung Windows. I have tried:
part 15-195 - 1-1/4" T-Lock Balance Shoe, Closed Cam and they will not work. Seems to be the right size, but the hook at the top will not hook onto the bar of the balance(?) and it will not fit all the way in due to the curved in the balance. Almost like the hook part at the top of part 15-195 is too thick.