A bayonet cap (not the screw in one, the other one) is one of the two most common lighting fixtures in Australia. Along with Edison screw mounts, the two fixtures account for the lion’s share of domestic lighting fixtures in the market. This is primarily because incandescent lamps for residential applications were only available in these two styles.
Bayonet cap design
The bayonet cap base and the bayonet cap mount are fastened together through a spring-loaded locking mechanism and ‘L’ shaped slots that hold the bulb in place.
How to identify bayonet cap sizes
Bayonet caps come in various sizes and can be identified by the designation ‘BC’, followed by a two-digit number. The number simply represents the diameter of the base in millimetres. The most common sizes of bayonet caps are BC15 and BC22, which have a base diameter of 15mm and 22mm respectively.
