All Thread (Hollow Threaded Bar) Male 0.5 Inch ( ½" )
Although M10 x 1 Fine is the "Electrical Norm" these days in both UK and Europe, the traditional size was 1/2". We keep only 2 sizes of 1/2" thread in stock now and they are both in brass, as most people using it really are working on keeping the restoration original.
Before starting any electrical work, always switch off at the mains. If in doubt consult a competent electrician