The ISO (International Standards Organization) has adopted these straight thread sizes for fluid ports on pumps, valves, cylinders, and other components. ISO Port Threads for Pumps, Valves, Cylinders, and Other Components *In the ISO metric system a decimal point is written with a comma instead of a period. ISO Standard Pipe Sizes (for both Parallel and Taper Threads) ISO Specification 228/1 Internal thread (one tolerance only}: “Pipe thread ISO 228/1-G1½” (for example).Įxternal thread (closer tolerance): “Pipe thread ISO 228/1-G1❚” (for example).Įxternal thread (with wider tolerance): “Pipe thread ISO 228/1-G1❛” (for example). ISO Specification 228/1 applies to pipe threads which do NOT make a fluid-tight seal on the threads.
Under Specification 7/1 there is no external parallel thread. Internal taper threads: “Pipe thread ISO 7/1-Rc 1½” (for example}.Įxternal threads (always tapered for ISO 7/1): Pipe thread ISO 7/1-R 1½˝ (for example}. Internal parallel threads: “Pipe thread ISO 7/1-Rp 1½˝ (for example). ISO Specification 7/1 applies to pipe threads which make a fluid-tight seal on the threads. If a fluid-tight seal is required a sealing element (washer or gasket) must be used. Internal parallel threads (Specification 228/1) can be mated to external parallel threads. They should not be mated with internal pipe threads except where a leaktight joint is not required. However, parallel external threads do not make a tight fluid seal on the threads and should not be used for jointing. Taper external threads (Specification 7/1) can be mated to either taper or parallel internal threads. Copies of ISO specifications can be purchased from the ANSI (American National Standards Institute). Information on inspection and gauging is in Part 2 of the same specifications. These specifications give information on thread form, machining dimensions, and tolerances. ISO Specification 228/1, 1982 issue, contains information on threads which do NOT seal on the threads. ISO Specification 7/1, 1982 issue, contains information on threads in which the fluid seal is made on the threads and covers both taper and parallel threads. Since there is only one thread pitch, the thread pitch is usually not specified and they are called out only by nominal size as noted below. Parallel threads, if a leaktight fluid seal is required, seal with a gasket, washer, or O-ring against the female seat. Taper threads seal on the threads themselves. ISO pipe threads, when specified, are assumed to be parallel unless a taper thread is called out.
Reamers are not strictly necessary but in the larger sizes they enable a better thread to be produced. Taper threads have a 1:16 taper and the same reamers can be used as for NPT threads. Parallel threads (also called straight threads) and taper threads. There are two variations of ISO pipe threads. Note: there is no ISO thread modification such as the NPTF (National Pipe Thread Fuel) for improved sealing between threads. Sizes start at 1/16˝ and go up through 6 inches. As with NPT threads, the nominal size does not represent true outside pipe diameter but in the larger sizes it comes very close. Pitch (the distance between threads) is expressed as the number of threads per 25.4 mm (1 inch). in inches, but with a slightly different thread pitch so the two systems are not interchangeable. ISO taper pipe threads are similar to the American NPT thread, having the same nominal sizes based on the pipe O.D. ISO metric machine threads should be used instead of pipe threads for mechanical fastenings such as bolts and nuts.īSP (British Standard Pipe) threads, using the Whitworth thread form, have been adopted as the ISO standard for pipe threads, and will hereafter be called out as ISO and not as ESP. Straight thread ports are shown on the back side of this sheet. However, except on very small ports, straight threads with O-ring seal may be preferred to pipe threads as component ports. An appropriate thread sealant can be used, if necessary, to ensure pressure-tight joints. These metric pipe thread sizes have been adopted by the ISO (International Standards Organization), and are primarily intended for pipes or tubes for screwing together or into ISO pipe ports on valves, cylinders, pumps, and other components.