The master socket contain a surge arrestor and an R/C circuit filter these are used by your service provider to get a fixed value resistance when they run line checks. Standard BT type socket with screw type terminals. Flawless Screwless design
– Master BT type socket
– Screw terminals
– Screwless low profile design with built in gasket
– Certified to BS 5733
– Minimum mounting box depth: 25mm