Edison screw (ES) is a standard socket for light bulbs. It was developed by Thomas Edison and was licensed in 1909 under the Mazda trademark. Normally, the bulbs have right-hand threaded metal bases (caps) which screw into a matching threaded sockets (lamp holders). For bulbs powered by the mains supply, the thread is connected to neutral and the contact on the bottom tip of the base is connected to live (hot).