Motor pulley 1 3/4" diameter (outside) with a 3/4" I.D. This pulley is to be used on clutch motors with a 3/4" shaft diameter. The diameter of the inside belt bearing surface is 1 1/16". Using a smaller pulley will slow a table mounted industrial sewing machine down and at the same time increase penetration power. Remember that changing to a smaller pulley will usually mean you need to order a new smaller drive belt. In this case it should still be a 3L size. Sailrite offers a flexible link type belt which can be adjusted in size by removing link sections.