Ring & pinion gear set, 3 to 1 high speed ratio, (39 tooth ring and 13 tooth pinion gear). 2 Piece set includes one large ring gear and one small pinion gear. Replaces standard ratio ring and pinion gears. Allows your Model T to run at higher speeds with lower RPM. These are the best quality gears, made in USA (These gears are not recommended for heavy model T's such as Sedans, Center Doors and Coupes.) For best performance use with a ruckstell rear end.