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    Default help identifying a (imperial) thread

    Dear all hi,

    I have this cap to replicate:



    The part is slightly worn and I don't have a blueprint of course, so I will have to identify it from measurements.
    Plus, since the part will screw on a ship, I have no way of testing the thread, it will have to work!

    So, using my thread gauge I found it to be 11 TPI. The gauge was not a perfect fit because the thread is a bit deformed, but I also measured with calipers and I'll stick to 11 TPI.

    OD measures exactly 44 mm! 1.732"

    I did try to identify this, apparently imperial thread, but with no luck. Could be my lack of experience with imperial threads, or the wear on the thread that misleads me, but I am at a loss....

    Any advice would be highly appreciated!

    BR,
    Thanos

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    Could it be a 1.5-11.5 national pipe straight mechanical (NPSM)? It could also be metric. Is most of the ship metric or imperial?

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    Quote Originally Posted by nt1953 View Post
    Could it be a 1.5-11.5 national pipe straight mechanical (NPSM)? It could also be metric. Is most of the ship metric or imperial?
    Hi, thanks for the reply.

    No, I am afraid it can't be this thread. Diameters on this NPSM are way too large.

    I am pretty sure the thread pitch is not metric! At least not any metric my gauge will measure or my lathe will cut....

    BR,
    Thanos

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    Bone up on pipe threads. A 1 1/2 pipe thread is considerably larger than 1 1/2 - but not so small as 1.732

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    Quote Originally Posted by johnoder View Post
    Bone up on pipe threads. A 1 1/2 pipe thread is considerably larger than 1 1/2 - but not so small as 1.732
    Hi there John,

    thanks for the reply.

    Well, that's the problem exactly....OD of any thread at 11 TPI I've seen is 'not so small as 1.732" = 44 mm.....

    (unless I didn't understand your suggestion correctly)

    Any more ideas?

    BR,
    Thanos

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    It is 1 3/8" BSP.

    You should be able to get BSP cutters in Greece, since it is also the ISO Metric thread standard. 1 3/8" isn't a common size, but the 11 threads per inch is common to a number of BSP thread diameters.

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    Quote Originally Posted by Mark Rand View Post
    It is 1 3/8" BSP.

    You should be able to get BSP cutters in Greece, since it is also the ISO Metric thread standard. 1 3/8" isn't a common size, but the 11 threads per inch is common to a number of BSP thread diameters.
    Thank you so much Mark!

    Just once again that the 'internet does not speak always the truth' : I checked here MARYLAND METRICS -- THREAD DATA CHARTS (7) (and not only here). Wasn't able to locate my thread....and there it is in wikipedia....

    I will grind a tool for this (the material to be machined will be brass) but why did you connect it to ISO metric? Isn't BSP 55 deg like Whithworth? That's what wiki says!

    Thanks again a million

    BR,
    Thanos

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    Any more ideas?
    Have a mm pitch gauge? How does 2.25 look? Better or worse than 11 TPI?

    I'd be interested in the answer to question above - is the ship mostly metric or mostly Imperial?

    Some givens.....

    It cannot be larger than existing simply because you and the end user have no clue of how sloppy or how snug the original fit up was

    You have to assume that it is possible that it was made to fit what was there at some point in the past, and does not necessarily conform to any standard

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    What is it out of as I have seen quite a few like it in pre-war Rolls-Royce engines and those are readily available?

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    Quote Originally Posted by thanvg View Post
    I will grind a tool for this (the material to be machined will be brass) but why did you connect it to ISO metric? Isn't BSP 55 deg like Whithworth? That's what wiki says!
    I have not researched the thread data, but I must say that in the photo it does look like a 55 degree thread - the threads look slightly too sharp to be ISO 60-degree threads. I'd find a Whitworth thread gauge and check.


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    Quote Originally Posted by thanvg View Post
    Thank you so much Mark!


    I will grind a tool for this (the material to be machined will be brass) but why did you connect it to ISO metric? Isn't BSP 55 deg like Whithworth? That's what wiki says!

    Thanks again a million

    BR,
    Thanos
    ISO "metric" doesn't mean always 60 degrees.
    DIN228 = IS0 228 standard = BSPP = 55 degree.

    why? only god knows..probably political compromise to lure brits into metric
    (probably goes back further than that, since GERMAN DIN228 standard is old as Metusaleh.

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    My Machinery's Handbooks shows a 1 3/4 - 10 as a UNS (special). Maybe the threads are pulled a little from over tightening? The tops of the threads appear truncated enough to make 1 3/4 possible.

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    Quote Originally Posted by johnoder View Post
    Have a mm pitch gauge? How does 2.25 look? Better or worse than 11 TPI?

    I'd be interested in the answer to question above - is the ship mostly metric or mostly Imperial?

    Some givens.....

    It cannot be larger than existing simply because you and the end user have no clue of how sloppy or how snug the original fit up was

    You have to assume that it is possible that it was made to fit what was there at some point in the past, and does not necessarily conform to any standard
    Hey John,

    my pitch gauge does not have 2.25 mm, nor does my lathe cut it, so I'll stick to the 11 tpi story, it suits me

    Regarding what the ship is, I realy have no idea...

    Thanks for the advice regarding copying the part, you are exactly right. Safest thing would be to make a female gauge that is a reasonable (a bit on the loose side if I may err) fit to the existing part and thread my new parts based on that. I don't have an idea on the fit of the part, so I am blind here.
    Regarding conforming to a standard, I was asked for 5 parts. I would like to hope that they didn't have to fit 5 of those, so it must be following a standard.

    Quote Originally Posted by Leadfootin View Post
    What is it out of as I have seen quite a few like it in pre-war Rolls-Royce engines and those are readily available?
    It's a big ship, no relation to Rolls whatsoever...

    Quote Originally Posted by Joe Gwinn View Post


    I have not researched the thread data, but I must say that in the photo it does look like a 55 degree thread - the threads look slightly too sharp to be ISO 60-degree threads. I'd find a Whitworth thread gauge and check.

    If it's a BSP (which we'll say it is), then is should be 55 deg. Thread gauge fits ok, but so does the 60 deg one (due to wear)

    Quote Originally Posted by MattiJ View Post
    ISO "metric" doesn't mean always 60 degrees.
    DIN228 = IS0 228 standard = BSPP = 55 degree.

    why? only god knows..probably political compromise to lure brits into metric
    (probably goes back further than that, since GERMAN DIN228 standard is old as Metusaleh.
    Totally right....

    Quote Originally Posted by FredC View Post
    My Machinery's Handbooks shows a 1 3/4 - 10 as a UNS (special). Maybe the threads are pulled a little from over tightening? The tops of the threads appear truncated enough to make 1 3/4 possible.
    No Fred, it's definitely no 10 tpi!

    Thanks for all the help to all!

    BR,
    Thanos

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    Quote Originally Posted by Mark Rand View Post
    It is 1 3/8" BSP.

    You should be able to get BSP cutters in Greece, since it is also the ISO Metric thread standard. 1 3/8" isn't a common size, but the 11 threads per inch is common to a number of BSP thread diameters.
    Your (the OP's) thread is 1 3/8" BSP. It is "standard" but not common.

    BSPP (the last "P" stands for Parallel) has been adopted by ISO and is now simply called G. Ref.: ISO 228.

    Maybe relevant but external G threads have 2 sizes of pitch diameter tolerances. A and B. B is exactly twice the size of A. If no tolerance is specified then it is always A.

    Whitworth pipe threads type G have only 4 pitches. 28, 19, 14 and 11. It is also the most commonly used straight pipe thread used in the world.

    Added: This thread type is almost always used with a gasket or an O-ring to seal.
    Last edited by Gordon B. Clarke; 08-21-2019 at 01:05 PM.

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    Quote Originally Posted by Gordon B. Clarke View Post
    Your (the OP's) thread is 1 3/8" BSP. It is "standard" but not common.

    BSPP (the last "P" stands for Parallel) has been adopted by ISO and is now simply called G. Ref.: ISO 228.

    Maybe relevant but external G threads have 2 sizes of pitch diameter tolerances. A and B. B is exactly twice the size of A. If no tolerance is specified then it is always A.

    Whitworth pipe threads type G have only 4 pitches. 28, 19, 14 and 11. It is also the most commonly used straight pipe thread used in the world.

    Added: This thread type is almost always used with a gasket or an O-ring to seal.
    Many thanks for the extra details.
    Have found fragments of it searching around today, with the forum's guidance.

    Many thanks again to all

    BR,
    Thanos

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    There is no way to get an accurate thread measurement from the OD. You can get close. If it is a standard thread, you can guess what size it is, but none of that is accurate. And you said it has to fit.

    USE THE THREE WIRE METHOD or A THREAD MICROMETER. That will give you the correct pitch diameter and then it will fit.
    Last edited by EPAIII; 08-22-2019 at 03:53 PM.

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    Quote Originally Posted by EPAIII View Post
    There is no way to get an accurate thread measurement form the OD. You can get close. If it is a standard thread, you can guess what size it is, but none of that is accurate. And you said it has to fit.

    USE THE THREE WIRE METHOD or A THREAD MICROMETER. That will give you the correct pitch diameter and then it will fit.
    You are most right on this of course....I would hate to have these parts coming back to me for 'adjustments', so I'll do what's necessary!

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    Quote Originally Posted by Gordon B. Clarke View Post
    Your (the OP's) thread is 1 3/8" BSP. It is "standard" but not common.

    It is also the most commonly used straight pipe thread used in the world.

    Added: This thread type is almost always used with a gasket or an O-ring to seal.
    - not common, right. It's not in my Machinery's Handbook (ed 29)....

    - had I known it was on a pipe and had I known '...most commonly used straight pipe thread...' I might have found it myself.
    Really now, since it was missing even from MH, what would be a safe place to search for this kind of stuff in the future?
    (apart from PM forum of course )

    - indeed, there is a (tapered) groove on the sealing face which, I would assume, is meant to accept an O-ring.

    Many thanks
    Thanos

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    Quote Originally Posted by thanvg View Post
    what would be a safe place to search for this kind of stuff in the future?
    (apart from PM forum of course )
    International Thread Standards has helped me more than once when I'm wondering some weirdo thread. Also not helpfull more than once..

    (talking about pain in the butt, SMS is quite common dairy equipment thread = Swedish Milk Standard!)

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    Quote Originally Posted by MattiJ View Post
    International Thread Standards has helped me more than once when I'm wondering some weirdo thread. Also not helpfull more than once..

    (talking about pain in the butt, SMS is quite common dairy equipment thread = Swedish Milk Standard!)
    Crazy stuff....

    I think I might just ask here if something strange (to me) pops up again

    BR,
    Thanos


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