Series 7 Mechanical Compression Fittings and Valves for cold water systems, rated PN 16 (with few exceptions) and available in diameters 16mm up to 125mm. Captive o-ring seal provides life time protection against leakage and requires no nut tightening to achieve full seal. Threads, where existing, are designed to ISO 7/1 "pipe threads where pressure tight joints are made on the threads", internal thread designation "Rp" (cylindrical) and external thread designated "R" (Tapered). We strongly recommend the use of PTFE tape in threaded connections or other appropriate sealing material