Product 4 cylinder future 1.Large 98 mm = 3.85 'hole wedge diameter 19 mm = 3/4 Drive wheel with a bore sized for a 3/4" (19 mm) drive shaft with a 3/16" keyway. It is also broached to use with keyed shaft or can be used with a smooth shaft with a flat ground on it for the set screw. A set screw is included. This wheel is domed (convex) in the contact area for proper belt tracking. 1 Medium 68 mm = 2,67 'hole 10 mm = 0.39' This wheel is domed (convex) in the contact area for proper belt tracking. 2 pieces Small 48 mm = 1,88 'hole 10 mm = 0,39'