This is a Brass BC Switched Lampholder with a 1/2" threaded fixing in the base.
This Brass Switched Lampholder comes with a 1/2" thread in the base. It also has a shade ring to hold a lamp shade with a 28-29mm diameter hole.
As this is a metal lampholder, ensure you use a 3 core mains flex to provide an earth connection to this lampholder.
Please Note: This 1/2" lampholder will NOT fit the 1/2" BSP gas pipe, BSP gas pipe is alot larger in diameter and is a totally different thread style.