Aftermarket On-Off Toggle Switch replaces Dewalt P/N 5130221-00, MK Diamond P/N 154310, Hubbell P/N HBL21SP, Husqvarna P/N 542193885 and Emglo P/N 5131519-00. Switches are commonly replaced parts in power tools. A switch handles all on/off and variable speed functions. They also have a role in electric breaking; they can momentarily reverse electrical polarity. Because switches use mechanical internals, they tend to degrade and wear out over time, eventually requiring replacement.