Gauging ISO 7/1 Rp Internal Threads?
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  1. #1
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    Default Gauging ISO 7/1 Rp Internal Threads?

    I kan't say that I have ever had a gauge straight pipe threads on any sort that I can think of, and I am asked to quote on threading a few flanges with a 1.25" ISO 7/1 Rp thread.

    Near as I can decipher, this is equiv of a BSPP thread?

    But even if that is the case, I can find oodles of ref as to the "size" of the [BSPP] thread, but nowhere does it tell me how to gauge it.

    I am getting conflicting info from a gauge source that I am either to use a GO/NO Go set of plugs, but also some ref to "supposed to use an Rc plug" (BSPT equiv?).

    Google doesn't find anything.

    Machinery Handbook doesn't seem to be willing to divulge.

    ???

    I've already got more time in researching this subject than it should take to produce 3 threaded holes!


    Also - I have ME ThreadPal, and he has BSPP in there, but not ISO 7.
    The two ARE the same - right?
    The only diff that I have found for sure is that ISO 7 has dropped the BSPP external, but they doo recognize the internal.
    ???


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    Think Snow Eh!
    Ox

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    I have no direct knowledge, but I was curious; did find this:

    "Pipe Threads. 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. An appropriate thread sealant can be used, if necessary, to ensure pressure-tight joints.

    However, except on very small ports, straight threads with O-ring seal may be preferred to pipe threads as component ports. Straight thread ports are shown on the back side of this sheet. ISO metric machine threads should be used instead of pipe threads for mechanical fastenings such as bolts and nuts.

    BSP (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. ISO taper pipe threads are similar to the American NPT thread, having the same nominal sizes based on the pipe O.D. in inches, but with a slightly different thread pitch so the two systems are not interchangeable. Pitch (the distance between threads) is expressed as the number of threads per 25.4 mm (1 inch). As with NPT threads, the nominal size does not represent true outside pipe diameter but in the larger sizes it comes very close. Sizes start at 1/16˝ and go up through 6 inches. Note: there is no ISO thread modification such as the NPTF (National Pipe Thread Fuel) for improved sealing between threads. Usually a thread sealant is required.

    There are two variations of ISO pipe threads. Parallel threads (also called straight threads) and taper threads. Taper threads have a 1:16 taper and the same reamers can be used as for NPT threads. Reamers are not strictly necessary but in the larger sizes they enable a better thread to be produced. ISO pipe threads, when specified, are assumed to be parallel unless a taper thread is called out. Taper threads seal on the threads themselves. Parallel threads, if a leaktight fluid seal is required, seal with a gasket, washer, or O-ring against the female seat. 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.

    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. ISO Specification 228/1, 1982 issue, contains information on threads which do NOT seal on the threads. These specifications give information on thread form, machining dimensions, and tolerances. Information on inspection and gauging is in Part 2 of the same specifications. Copies of ISO specifications can be purchased from the ANSI (American National Standards Institute).

    Taper external threads (Specification 7/1) can be mated to either taper or parallel internal threads. However, parallel external threads do not make a tight fluid seal on the threads and should not be used for jointing. They should not be mated with internal pipe threads except where a leaktight joint is not required.

    Internal parallel threads (Specification 228/1) can be mated to external parallel threads. If a fluid-tight seal is required a sealing element (washer or gasket) must be used.

    ISO Specification 7/1 applies to pipe threads which make a fluid-tight seal on the threads. The correct way of calling them out is:

    Internal parallel threads: “Pipe thread ISO 7/1-Rp 1½˝ (for example).

    Internal taper threads: “Pipe thread ISO 7/1-Rc 1½” (for example}.

    External threads (always tapered for ISO 7/1): Pipe thread ISO 7/1-R 1½˝ (for example}. Under Specification 7/1 there is no external parallel thread. (See Specification 228/1 ).

    ISO Specification 228/1 applies to pipe threads which do NOT make a fluid-tight seal on the threads. The correct way of calling them out is:

    Internal thread (one tolerance only}: “Pipe thread ISO 228/1-G1½” (for example).

    External thread (closer tolerance): “Pipe thread ISO 228/1-G1½A” (for example).

    External thread (with wider tolerance): “Pipe thread ISO 228/1-G1½B” (for example)."

    from ISO Pipe Thread and Port Thread Sizes - Womack Machine Supply Company


    apologies if you've already seen it. Seems, as you suspect, to gauge with BSP gaging.


    additional:

    BSP Thread Type – British Standard Pipe

    This is a standard thread type that has been adopted internationally for interconnecting and sealing pipe ends. You’ll find it used all throughout Europe. There are two types of BSP threads, BSPP and BSPT. BSPP refers to parallel or straight threads. Meanwhile, BSPT refers to tapered threads. Sometimes BSPP threads are referred to as G threads and BSPT threads as R threads. Are you confused yet?

    Note: JIS tapered pipe thread (PT thread) is interchangeable with BSPT thread.
    Last edited by machinistrrt; 05-03-2021 at 01:54 PM. Reason: added info

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    apologies if you've already seen it. Seems, as you suspect, to gauge with BSP gaging.
    But IDK how to gauge BSPP either.

    Again - I have been given conflicting info as to whether it is s'posed to be a GO/NO Go plug set, or by using a tapered plug (that would presumably seat at the step depth, but IDK)



    Edit:

    Well, per E-bay, there seems to be several Go/No Go plugs for BSPP, which appears to be the same as the ISO call-out.

    So, I'm not sure where the "Chech with taper plug" statement came from?
    Has anyone ever used, or heard of being used - a taper plug for this app before?




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    Rp is a strange one.

    It is a parallel female thread, but both Rp and Rc (tapered female) mate with the same tapered male thread (R), so use the same tapered gauges.

    G and Rp are almost the same. The pitch diameter tolerance is tighter for G, which means that if your thread gauges good on PD with a G gauge, it is also good on PD for Rp in all cases. Not vice versa though.

    The main difference is the minor diameter, which is smaller on Rp than G.

    Basically, Rp and Rc use the same gauge, which is a taper step limit gauge. G uses parallel go/no-go gauges, which can be used to gauge an Rp thread if you know what you're doing and measure the minor separately.

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    Well, that should be a cresting insert eh?
    (spec'd rads on crests?)

    The ID should fall in-line?


    Thanks for piping up!
    I guess that gives credibility to the conflicting info that I was git'n.



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    G PD 40.431-40.611
    G Minor 38.952-39.592

    Rp PD 40.251-40.611
    Rp Minor 38.772-39.132

    You can see there is overlap.

    Theadform on both is basic 11 Whitworth, so yes a standard full profile 11WH insert should get you there with some care.

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