These lampholders are easy to use and hold shades well. Ideal replacements for plastic equivalents and will invariably fit in the same space as the plastic version. Mounts on a standard 10mm all thread.  Fits a 40mm shade hole. Available in a wide number of finishes this lampholder is tough and durable and will outlast the plastic ones by years. They usually require a 3 core flex as they need be earthed, unless the fitting to which they are attached is earthed elsewhere and passes the electrical safety test.