Designed to turn stock 5-speed transmission into a 6-speed. Reduces vibration that creates wear. Creates a more relaxing cruising speed. All gear sets use 2.94:1 close-ratio 1st gear that widens bike's speed range in 1st gear and lessens the rpm drop when shifting into second. Overdrive 6th gear (.86:1 ratio) lowers engine rpm by almost 475 at 75 mph. Gaskets and seals included. Made in the U.S.A.. Requires speedometer sensor block-off plate kit; if speedometer is not driven from transmission, then two block-off plates kits are required.. Trap door extends 3/8" farther to right than stock part. Alteration to some parts that attach to or around the trap door may be required.. Requires speedometer be recalibrated..