12mm XR50 CRF50 XR CRF 50 Chain Adjuster 125cc Pit Bikes Brand New!! Never Been Used or Installed!! This item fits most  Honda XR50, CRF50, XR70, CRF70 All similar China made pit bikes like 70cc, 110cc 125cc. This item ensures CHAIN TENSION AND ALIGNMENT. It prevents excess wearing of the sprocket, chain derailment, and prolong chains's life If you don't have the proper chain tension, the chain will get lose or break. Even worst, it will damage the side cover and the stator-plate.