The adapter ring is an adjustment ring that aligns the outer diameter so that the grips "XCH28MT-K15BK" and "SFG-K15RC" for BF nut 15 can be used with KN16 (KDPS-KN16/ASH) without any steps. It is also possible to use the KN16 grip (ALH15-KN16 / MCH series) with the BF Nut 15 by attaching the ring upside down. * BF nut 15 = Hood nut used for TCP-FBCSK15 and TCP-NHSSK15