This is a Old English BC Switched Lampholder with a 10mm threaded fixing in the base.
This Old English Switched Lampholder comes with an internal earth connect rather than one on the side. It also has a shade ring to hold a lamp shade with a 28/30mm diameter hole.
Comes complete with a shade ring.
As this is a metal lampholder, ensure you use a 3 core mains flex to provide an earth connection to this lampholder.