For 3 1/8" To 4" interior diameter bores ? 180-240 grit for fine blending, finishing and polishing ? Use with Bpm-4 mandrel part no. 08834154183 ? Extension mandrels are available for deep holes ? 4 Abrasive packs 1-1/2 In. wide, bonded to hub ? Bore polishers are used for deburring, cleaning and polishing of the interior diameters of cylinders, tubes and hydraulic fittings. The flaps automatically adjust to the inside diameter, polishing the entire surface with one pass. A self-centering, spring action design gives a fast and easy way to handle all inside diameter jobs.