Shimano FC-M8120-1 XT Boost Crank Arms - 12 Speed. 170mm length Q-factor: 178mm Chainline: 55mm chain line works with 148 O.L.D. (Prioritizes frame and tire clearance) These are meant for a Boost spaced modern mountain bike. Direct mount chainring (not included). Lock ring, spacers and crank arm fixing screw included. These are used but in excellent condition with only a couple of minor dings and scratches