Bottom Turn Knob Lamp Sockets were frequently used on lighting in the mid 20th century. This practical design can be used vertically or horizontally. Cord exits from bottom side of socket.
2 piece unit: socket interior with screw terminals, fits inside husk. Outer husk is made of bakelite, an early form of plastic, produced from a synthetic chemical resin. Bushing unscrews from 3/8" - 1/8 IP threaded nipple to secure socket to lamp.
Before making any changes to electrical fixtures and/or lamps:
Disconnect plug/wire from the electrical source.
Turning lamp off will not protect you from electric shock.
If you are unsure how to safely proceed contact a licensed electrician.