This is a replacement barrel housing that holds the on/off valve part of a shower mixer valve. The part includes faceplate securing nut and rear fixing nut as photographed.
Commonly found on 3 dial shower mixer valves on brands such as Aqualusso, Opus, Alto, Lisna Waters, Aquaplus, Vidalux, Insignia and many many more.
Barrel Diameter: 28.8mm
Barrel Height: 37.6mm