WISECO replacement ring set (CDM) * CDM sets consist of two ferrox-coated ductile iron, internally notched compression rings. * Suitable for CHROME, NIKASIL, and ELECTROFUSION liners. Please note: Only WISECO replacement ring sets may be used on WISECO pistons. The ring type and bore size (mm) is stamped on the dome of the piston. Refer to this information to order the correct replacement rings. Ring styles cannot be interchanged.