The Sherline multi-wrench was designed to combine the four hex head fastener sizes used on Sherline lathes and mills into one handy tool. Sizes are: 1/4", 7/16", 3/8" and 11/16" (17mm). The tool itself is cut from 1/4" steel plate and has a tough black oxide coating to keep it from rusting. Keep it handy and you can make any needed adjustment on a Sherline tool without having to search through your toolbox for the right size wrench.