Will fit Shimano quick release rear Axle and some solid rear Axle: 4.6mm thick. Most Shimano solid rear Axle have 3/8″ x 26tpi threading, but some have 10mm x 1mm axle threading (the same as a Shimano quick release axle). A good way to determine whether your Shimano solid axle has 10mm or 3/8″ threading is to take a nut from that axle and see if it will thread onto a Shimano quick release rear axle. If the nut threads onto the quick release axle, the solid axle the nut came from has 10mm threading. If it will not thread on, the solid axle the nut came from has 3/8″ threading, which is slightly smaller.