A cordless impact driver may look like a cordless drill, but there are key differences. For one, the impact driver generates about four times the torque of a same-size drill, thanks too a spring-loaded cam and gear mechanism that kicks in when driving gets tough. Roland Johnson found that the impact driver comes in handy for jobs such as driving large screws, drilling big holes, and turning nuts and bolts. In fact, he found a lot to like about these tools: compact size, light weight, added torque, quick-change chuck, and improved driving control.

From Fine Woodworking #188