Telephone secondary socket fits standard 1 gang 25mm back box. Specifications: Sockets: BS 1363:Part 2:1995 250V 13A. Switches: BS 3676:Part 1:1989+AMD1. 250V 10AX rated.DP Switches: BS 4177:1992 25V 45A + 13A Socket.Fused Connection Unit: BS 1363: Part 4: 1995 +AMD1 250V 13A.2W Dimmers: EN 60669-2-1:1996, EN 60669-1:1996 (excluding clause 104.3) 250V.