Depending on the kind of projects you take on as a professional or as a DIYer, you might find yourself in need of a rotary tool. These are designed to make a variety of physically-intensive and time-consuming tasks – such as grinding, polishing, and sanding – much easier and more efficient. As such, they’re a must-have part of any competent craftsman’s tool kit.

However, rotary tools are more of a tool class, rather than a specific tool you’d pick up at the hardware store. In fact, if you did ask for one at a hardware store, you might then need to pick between a Dremel and a die grinder. 
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https://handymansworld.net/die-grinder-vs-dremel/