3-Way Mogul Base
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Mogul Lightbulbs
Mogul lightbulbs, often used in antique Stiffel lamps, are large, oversize, bulbs which screw into an oversize base. They are often 3-way bulbs, and they are often of PS / pear shape / pearstraight style (a longer than usual straight shape from the socket to where the bulb becomes rounded) but "mogul" does not imply "3-way" or "PS" nor vice versa.
Adaptors are available to allow mogul bulbs to be used in otherwise standard sockets, and for standard size bulbs to be used in mogul sockets.