The 8" & 12" bells listed have been reviewed by the U.S. Coast Guard and comply with C.G. 169 Regulations for sound signal appliances as required by Annex III paragraph 2 of the '72 colregs. The 8" bells are for use on vessels under 20 meters (65.6 ft.) in length. The 12" bells are for use on vessels of any length. #150 series is cast bronze (polished or chrome), heavy weight, removable, CG approved #158-12 is cast bronze (plain), heavy weight, fixed mount, CG approved #159 series is stamped brass (plain or chrome), removable, not CG approved