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, 2-1/8 in Bore Dia, 2.7657 in Small End/2.875 in Large End Barrel Dia, 4-1/2 in Hub Dia, 3-3/8 in Bolt Circle, 4-1/8 in Flange Dia, 0.53 in Flange Thickness, 3 Bolt Holes, 3/8-16 x 1-1/4 in Screw, For Use With: MST® Sprockets and HQ1/HCQ1 Weld-On Hubs, 2-1/2 in Overall Length, 1/2 x 1/4 in Keyway, Ductile Iron