Abstract: An attachment is provided for a tool with a rotary cutting element. The attachment enables an operator of the tool to determine when sufficient stock is removed from the wall of a slot to obtain the proper slot width and includes a gauging element extending longitudinally and generally parallel to the rotary cutting element, said gauging element being of width slightly less than the desired slot width. A cutting edge portion of the rotary cutting element protrudes from the plane of one of the elongated surfaces of the gauging element so that stock may be removed from a slot wall while the gauging element trails behind the cutting edge in the slot. In preferred form, a guide is located 180 degrees from the gauging element so as to precede the rotary cutting element into the slot and control the depth of cut thereof along the slot wall.