Hozelock 2181 Non-Return Valve Tap Connector 1/2 - 5/8in BSPThis Hozelock 2181 Non Return Outdoor Tap Connector is an all plastic double check valve, which connects to outside taps and prevents backflow into the mains water supply. Made from high quality materials for a long leak free life, it is suitable for all 1 2 inch and 3 4 inch BSP taps. Specifications: Screw Thread: 1 2in BSP (21mm), 3 4in BSP (26. 5mm). Connection Type: Male.