Fixing for wood.
With a backplate which is a Brass plate with 3 fixing holes to fix it to the wood, it is one of the easiest fixing methods as long as its wood you are fixing to. It comes with a threaded fixing for the lampholder in the middle and a choice of 10mm or 1/2" fixing.
Can be used on a solid material like metal but you would need to use nuts and bolts to hold the plate in place.
Use a 3mm countersunk screw.