This 9" guard is required when using 9 inch type 28 grinding wheels on Milwaukee grinder models 6080-20, 6081-20, 6082-20, 6086-20, 6088-20 and 6089-20. It can be used with grinding wheels with threaded hubs. Nylon washer 45-88-8466 is recommended to be used with threaded hub wheels to assist in removing wheels from spindle after hard use. No tools are needed to attach this guard to the listed grinders. The guard can be rotated around the spindle to achieve optimum protection for the operator.