Jno Brown side lamp font, model #100, 105, 110, and 115. (Holds oil for the light)
Highly polished, solid brass
This same font was used on both side lights and tail lights.
The flat part of the bottom measures 3-1/2" in diameter. The top of the neck measures 2-9/16" in diameter. Has four pins around the top neck that hold it to the body of the light.