This is the famous Kahler 6 string locking nut with String Director. It has a width of 1 5/8" (41mm) with a 12" radius. All of the Kahler string director (SD) locknuts, since the dawn of time, have used the top loading, #9525 clamp plates with the offset hole. The clamping screw is screwed down onto the the clamp plates using a 3/32" hex key for the cap type screws #8440, as shown, or a 1/8" hex key for the taller hex/slotted screws #5441 screws. The string director is mounted on the base just behind the clamping plates thus eliminating the need for a string bar or string trees. Rounded string bumpers help guide the strings through the clamp plates and on toward the tuners without snagging which greatly reduces risk of string breakage between locking point and tuner. The string director also prevents string from rubbing on the locking screw under the pad. FYI: These are now being manufactured with no Kahler stamp on the string director. Your shipped locknut may, or may not have the "Kahler" stamp on it depending on when the stock stamped pieces run out.