This Brass 10mm Backplate is ideal for fixing a lampholder that has a 10mm screw fixing in the base. The Brass 10mm Backplate has 3 screw holes to fix to the wood (fixing screws not included).
The backplate is 25mm in diameter.
Why not add a nut cover to the order to cover the 3 screws. This backplate can be used with a male / female spacer id additional height is required for the lampholder.
Screw fixing for these take 3x16mm countersunk for wood but other types of fixings would be needed for other matereials.