Thanks Jonathan, I was trying to find pulley sets that had the same centre distance so I could make my motor mount future proof and be able to change the ball screw ratios by just using different pulleys.

Hope you don't mind but used yours as a base to do a comparison tab? I've attached my addition in case it helps anyone else but please feel free to remove it there's a problem.

CheersBelt centre distance calulator3.xlsBelt centre distance calulator3.xls