This is a Brass BC Switched Lampholder with a 10mm Baseed fixing in the base.
This Brass Switched Lampholder comes with an internal earth connect rather than one on the side. 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.