Made by Jims USA this tool makes measuring piston ring end gap faster and more accurate. The flanged design allows the piston ring to fit exactly square into the cylinder bore. Jims claims that this is the first tool that is designed to test the oil ring gaps by a proprietary cutout feature. Just install any ring, top, 2nd or oil control rails on the tool and then into the cylinder bore and view the key slot. Use a feeler gauge to get your end gap measured. Each side of the tool is made for checking standard size piston rings.