Bayonet light fitting definition/explanation

Bayonet is the term used to describe a lamp holder or light bulb that uses 2 pins to lock in place. Also known as Bayonet Cap (as opposed to one with a screw thread known as an Edison fitting).

The pins on a Bayonet Cap bulb “twist and lock” into the two slots in a Bayonet Cap Lampholder.

There are 2 main sizes of Bayonet light fitting:

• Bayonet Cap – BC – B22d
• Small Bayonet Cap – SBC -B15d

The numerical values, B22d and B15d relate to the measurement in millimetres across the light bulb cap. B22d = 22mm and B15d = 15mm.