The Merit BPM-4 mandrel securely mounts bore polishers with a 1/2"-20 male thread onto a grinder that accepts a 1/4"-diameter shank. The one-piece mandrel design has a knurled portion for increased grip when installing and removing the polisher and is made of steel for strength and extended tool life. The mandrel has a threaded end that accepts the bore polisher, and it has a 1/4"-diameter shank that inserts into a grinder's chuck.

Merit Abrasives manufactures abrasives for the deburring and finishing industries. Merit, founded in 1945 and headquartered in Cleveland, OH, meets International Organization for Standardization (ISO) standards 9000 and 14001.