? For 4 1/4" to 5 1/4" interior diameter bores ? 180-240 grit ? For fine blending, finishing and polishing ? Use with BPM-8 mandrel part no. 08834154184 ? Extension mandrels are available ? For deep holes ? 8 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.