This special 12 volt light bulb fits in a standard household size screw-in socket. The official name of this style base is "medium."
Although it looks like a regular light bulb, it is not for use in your home. Do not attempt to use this bulb with 110V current or it will burn out immediately. However, if you have a light fixture that was designed for 110V current and you want to use it on 12V current, this bulb will let you do it.
This is a 25W frosted bulb. It draws approximately 2 amps. Overall, the bulb is 4" Long. Diameter is 2-3/8".