The speed of a rotary tool is measured in rotations per minute (rpms), and refers to how quickly the tool can spin an attachment. Most rotary tools have either set speed settings—two or three is common, although some have as many as six speeds—or a variable speed control that lets you choose the exact speed desired. Typically, a rotary tool has a speed range of around 5,000 rpms up to 35,000 rpms.  As a general rule, you’ll want to use a slower speed when working on delicate materials or materials that could melt, such as plastic. You’ll also want to use a slow speed for polishing, buffing, or any task that involves an attachment with a brush. Higher speeds are best for tasks that involve cutting or sanding. But always keep in mind that no matter the task, you should start off slowly and gradually turn up the speed. This allows you to maintain the best control of the rotary tool.