The damper rod has a 22mm 12-point socket in the top which this tool engages with to prevent it from spinning when loosening and tightening the damper rod bolt. This tool is to be used with a relatively thin-walled (so that it will fit inside the tube) 22mm socket, extension, and your choice of drivers (breaker bar, ratchet or tee-handle). Install the damper rod bolt with a new sealing washer 509-23158-L0-00 GASKET and, using a torque wrench, torque to 22 ft.-lbs. (30 Nm). Additional information can be found on page 5-25 of the factory Yamaha service manual.