This is a Aged Brass BC Switched Lampholder with a 10mm threaded fixing in the base.
This Aged Brass Switched Lampholder comes with a small locking screw in the stem to ensure it will not work loose when fitted to a 10mm male thread. It also has a shade ring to holde a lamp shade with a 30mm diameter hole.
Comes complete with a shade ring and will fit a shade with a 28-29mm hole.
As this is a metal lampholder, ensure you use a 3 core mains flex to provide an earth connection to this lampholder.