Countries that formed part of the former British Empire – such as the United Kingdom, , Australia, New-Zealand and India – use bayonet fittings rather than the Edison fittings. Standard bayonet fitting size is B22, also specified as BC. The bayonet fitting was designed by George Lane-Fox, the competitor of Thomas Edison (the inventor of the light) and further developed by the US Brush Electric Company around 1870. The standard fittings have two radial pins on the side of the metal sleeve.
The major benefit of a bayonet fitting as compared to a regular Edison fitting is the fact that the bayonet fitting cannot get unstuck through vibration. In some cases, the pins on the metal sleeve are not straight across from one another; this is done when the lamp may be positioned into one direction. The bayonet fitting is indicated by Ba (Bayonet), followed by the diameter of the fitting. In addition to the standard Ba22, or B22 (Bayonet Cap – BC), there is the smaller Ba15 type (Small Bayonet Cap â€“ SBC). The additional ‘s’ or ‘d’Â (undercast) indicates whether the lamp has a single or double contact point.
The Calex range includes the Ba15d and B22 fittings.