We use standard 'British Standard Pipe' thread sizes used throughout the sanitary industry. 1/2" for shower hose, valves that screw into sink or basin taps and UK connectors. 3/4" for bath tap rigid tails, valves that fit into bath taps. 1.25" for basin wastes. 1.5" for bath & sink wastes. Minimum water pressure 0.1 bar and maximum 5 bar.