Check the listing for details. 1 Gang 35mm Single Dry Lining Plasterboard Cavity Wall Mounting Back Box. Condition: New. Listed at 5.65 USD. The DLB351 Single Gang 35mm Drylining Box by ESR is ideal for fast fixing into cavity wall structures, dry lining partitions and plaster board up to 15mm thick. Large flange around front prevents the box from slipping into cavity and matches profile of accessory front plate. Manufactured from flame retardant thermoplastic, keeping electric elements protected in the event of a fire, even after the structural integrity of the wall has deteriorated. Tough yellow/red nylon lugs have large bearing faces for superior strength and are specifically designed to ensure ease of clamping dry lining boxes with partitioning wall. Knock out Cable entries to both sides, top & bottom in addition to a 20mm Knock out to the back of the box. To complete the installation of this product and achieve a neat plas.