The Park Tool Double-sided bottom bracket lockring hook spanner is a must in any bike mechanic's tool box. One side is a single hook, the other is a hook spanner with 3 notches for better engagement in the lockrings. The three-hook end will fit 3-notch lockrings with a maximum outside diameter of 46mm, and minor diameter (in the notches) of 40mm. NOTE: The HCW-5 is designed for bottom bracket lockrings. For fixed gear lockrings, use the HCW-17.