This aftermarket Trigger type switch with lock has 4 internal terminals and replaces Milwaukee 14-78-0550 switch. It is a 10A-125V Over Hang Trigger Switch that comes with Lock and integrated dust proofing commonly used in high rated bench top and power tools.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.