Booster thru-axle hub spacer kits are designed to give your non-Boost front and rear thru-axle hubs the boost they need to fit any Boost-compatible frame or fork. Kit includes Center Lock Adaptor, allowing riders to use 6-bolt rotors on Shimano Center Lock compatible hubs. - 6mm spacer kit adapts 142 x 12mm rear hub to 148 x 12mm - Includes 6mm adapter to 6-bolt rotors - Includes external spline lock ring for thru-axle compatibility