Mandrels are used to mount different accessories to use with your Dremel rotary tool. The 401 Dremel Mandrel features a 1/8 In. (3.2 mm) shank with a screw-like head used primarily to hold soft and pliable accessories like polishing bits. The accessories can be threaded onto the mandrel simply by screwing the accessory into place. The 401 Mandrel can be used with the 414, 422 and 429 cleaning and polishing accessories.