Arm Material: aluminum Arm Length: 165mm, 170mm, 175mm, 180mm Chainring Sizes: 36T, 34T, 32T, 30T, 28t Bolt Circle Diameter: direct mount Rings: 1 Shimano's XT FC-M8130 1x Crank Arms feature a lightweight design for aggressive trail riding. Direct mount chainrings and a special gear tooth profile for improved chain retention are included with a completely new design, along with a 181mm Q-factor.