Bayonet base miniature light bulbs have a bottom contact and side lugs that lock the base into a matching bayonet socket. Also known as bayonet cap lamps, they resist vibration for a more secure hold than 2-pin lamps. They supply the light source for specialized applications ranging from indicator and signal lights to appliance and projector lights. Their trade number provides a reference to find a replacement bulb for a specific application. The number may be printed on the lamp itself or in its instruction manual.