This specification covers cast sound-signalling bells, together with bulkhead mounting plates for the smaller bells, for use on ships, boats, and other marine craft, for compliance with the rules in the convention on the International Regulations for Preventing Collisions at Sea (commonly called Colregs). See Appendix X1. Bells and bulkhead mounting plate shall be sized as indicated in Section 4 (see Appendix X2). For consistency with International Regulations, all measurements are in SI units.