OM488-20 Counterbores (1/4” Shank) or spotfacers are used to assure a flat seating surface for fasteners or mating parts that are 90° to the axis of the hole. Counterbores are furnished without a ”corner radius” unless specified. Solid carbide and carbide-tipped counterbores, reverse countersinks, and reverse spotfacers are also available on request.