Fits into existing 5-speed cases; lowers the rpm at cruising speeds. Includes a black trap door, 6-speed gear set (3.24:1 1st gear/0.86:1 6th gear), 28-tooth motor sprocket, longer primary chain, adjusting shoe, fixed spindle-shift drum and anti-overshift ratchet shift pawl assembly. All gears are full-width Baker ground gears; 4th, 5th and 6th gears are helical for silent operation. Includes easy-to-follow instructions. Made in the U.S.A.