This transmission main shaft counter gear set is designed for horizontal engine dirt pit bikes with 140cc, 150cc, and 160cc displacements.It is compatible with YX140, YX150, and YX160 engine configurations.The part fits engines featuring a 56mm bore including models 1P56YMJ ZR, 1P56FMJ W063, 1P56FMJ-5 W150-5, and a 60mm bore including models 1P60YMJ ZR, 1P60FMJ W150-2, 1P60FMJ W150-4V.It also suits 160cc engines with a 60mm bore such as 160 FMK W160-2 and those with a 62mm bore like 1P60FMK W160-4V.This component serves as a functional replacement for various pit bike brands including KAYO, BSE, Bosuer, Xmotos, Apollo, Orion, Rusi, SSR, SDG, GPX, GMX, Pitsterpro, Mobster, Thumpstar, and YX series motorcycles.Installation restores the shifting mechanism of the gearbox assembly.