Doorstop Lamps      

Some commonly thought to be doorstops are not doorstops at all but Doorstop Lamps
The Critical Characteristics of a Doorstops Lamps is that they look like any acceptable doorstop
except they always have a U-Groove on the back to hold the Electric Bulb.

 
This U-Groove holds a Hollow Threaded Rod secured by 2 nuts that sandwich this metal projection.
The Light Scocket screws onto this threaded rod and the electric chord goes thru the hollow part of
the rod & plugs into the wall..
Probably, the main reason these get confused with actual doorstops
is that usually the Threaded Rod, the Bulb & the Electric Chord are missing
and the only distinguishing feature is that U-Groove protuding from the backside
.