Murray Pulley part# 91943 has an inside diameter of 5/8" and an outside diameter of 5-1/4". The inner surface of the mounting hole is machined for a splined shaft. We were unable to find a list of model numbers for this part, but it was used on 40600 series riding mowers from 1989 and up. Please refer to your owners manual or a parts breakdown for your model, to assure that this is the correct part for your machine, before you order.