MST® bushings are easy to install and remove. They are split through the barrel and have a taper to provide a true clamp on the shaft. They are keyed to both the shaft and the hub to help during \"blind\" installations. Martin MST Bushing, Standard, 2-1/2 in Bore Dia, 4.418 in Small End/4.625 in Large End Barrel Dia, 6-3/4 in Hub Dia, 5-3/8 in Bolt Circle, 6-3/8 in Flange Dia, 3/4 in Flange Thickness, 3 Bolt Holes, 1/2-13 x 2-1/4 in (Cap Screw)/3/8-16 x 3/8 in (Set Screw) Screw, For Use With: MST® Sprockets and HS1 Weld-On Hub, 4.38 in Overall Length, 5/8 x 5/16 in Keyway, Ductile Iron