New Genuine Dremel motor brushes for use with Model 275, 285, 395 and 595* rotary tools (Type 3*, 4*, 5* and 6 only). They can also be used with the Dremel® Contour Sander (Type 1 and 2). item 90930 Motor brushes consist of a coiled spring of metal with a piece of carbon at the end. They go under the brush cap and rest on the armature, providing the electrical connection to keep the tool running. These easily replaceable accessories also help extend the life of the tool. You should check both motor brushes after every 50-60 hours of use. Simply unplug the tool, open the brush caps and remove the carbon piece from the holder. If there is less than 1/8" of carbon left on either brush, they both should be replaced.