Beautiful, British Made and very traditional.  Used quite extensively on real antique French fittings.  Does not have an earth, so you need to make sure you have a good earth connection on the stem of the fitting you are restoring.  M10 thread entry.  Be aware you need to wire the lampholder first before connecting the flex the other end as you have to screw the whole lampholder down first so you need the wire free to rotate.  This is one of the narrowest lampholders on the market and is often used within delicate candelabra sleeves.

SBC / B15

10mm Threaded Entry, Not Shade Compatible

Width: 20mm, Height: 46mm