Dry Lining Box 1 Gang 35mm

A dry lining box is a plastic or metal box used to mount electrical outlets and switches onto a wall.

The "1 gang" designation indicates that the box is designed to accommodate a single electrical accessory, such as a single light switch or electrical outlet. 

The "35mm" measurement refers to the depth of the box, which is the distance from the front face of the box to the back. A 35mm dry lining box is a standard size used in the UK for mounting electrical accessories onto plasterboard or drywall.