This is a replacement counter shaft reduction gear set for GY6 125cc and 150cc , compatible with 4-stroke engines including 152QMI and 157QMJ models.The set includes two pre-pressed gears: a large gear with 42 teeth and an outer diameter of 29 mm, and a small gear with 13 teeth and an outer diameter of 69 mm.Both gears are designed for a 15 mm shaft diameter.This part restores specifications and maintains the factory gearing ratio when installed on vehicles with matching tooth count.Compatible with , mopeds, ATVs, and go-karts from brands including Kinroad, Twister Hammerhead, Carter Talon, Dazon, Roketa, DUNE, Kasea, KPX, SUNL, Aimex, Alpha Sports, Avanti, Bam X, Baotian, Bashan, BMS, BMX, Boreem, Runner, Cool Sports, Diamo, E Ton, Fushin, Fly, GMI, Hensim, Hi-bird, Ice Bear, Jackel, Moto, JCL, Peace, JM, Jonway, KMD, Lance, Linhai, Longbo, Fuxin, Maxtrade, MDI, Meitien, Motofino, Motorino, NST, Panterra, Panther, Qlink Yiben, Red Streak, Schwinn, Seaseng, Strada, Tank, Terminator, Tomberlin, TNG, United Motors, Verucci, Wildfire, X-Treme, Yamati, and ZNEN. Note: This part is made by an independent vendor.Any brand/model mention is for compatibility purposes only.