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  • What Size Thread?

    Major diameter is 1.803, but the fit is a bit loose, 18 threads per inch.
    My MH is at home, can someone tell me if these are standard threads or not?
    Thanks!

  • #2
    1 13/16" x 18 = 1.8125" x 18

    or

    46mm x 1.5mm pitch = 1.811" x 16.93 tpi
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      Thanks! So it IS a standard UN?

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      • #4
        Joel. MH does not show 1-13/16 X 18 as a standard. UN 1-13/16 X 16 and 1-13/16 X 20 are.
        It(MH) also shows that there is no 46 X 1.5mm.
        45 X 1.5 and 48 X 1.5 are standard.

        Whats this for if I may ask?

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        • #5
          It is a valve adapter for a firefighting nozzle, kinda hard to explain.
          I have one in front of me, and need to get it spec'd out on a print. I was hoping it wasn't a "unique" thread.

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          • #6
            Joel. I wonder if this isn't a 'standard' of the fire fighting equipment industry. It sure would make it difficult to buy anything 'off the shelf'

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            • #7
              That sounds close to schedule 80 pipe thread. What is the material?

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              • #8
                Rusty, the NH/NST threads are the only ones I have ever come across as standard fire threads. They are usually big, and always coarse. This part comes off a production valve with no real reason not to be standard. They are definitely 60*, 18 TPI. It looks like the minor dia is around 1.715.

                It is made of aluminum Ken.

                Thanks guys.

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                • #9
                  Pipe thread in this size range is 11-1/2 TPI regardless of pressure rating.
                  I see no fire hose threads as fine as 18TPI in Machinery's Hand book. Most are coarser, but none smaller than 2-1/2" are listed. It can be anybody's guess with a lot of these, as alot are proprietary.
                  Jim H.

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                  • #10
                    It's quite possible it's an oddball thread used to prevent the competition form supplying parts and attachments and force single source purchasing from the maker. There's as many standard in older fire apparatus as there were apparatus manufacturers.

                    Fire fighting gear has gone a long way towards a standard for hoses, nozzels, and connections here in the US but everything between the hydrant suction hose pumper and the pressure fitting is still a mish mash and a machinist's sinecure of wierd threads and fittings.

                    That's said yours is not a NPT nor is it a UN thread. It's a UNS (s for special). Check the pitch diameter across three wires to verify that it is indeed a UNS thread and from that data you can make mating threads and fittings for it.

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                    • #11
                      Yea JC, I let my fingers talk before the brain was working. What I meant was these fine threads are used on high pressure fittings like gas and hydraulic. Somebody with a book should be able to look it up. The size listing would be about 1" ID for 1.8 OD. Maybe the thread used on AN fittings?

                      [This message has been edited by CCWKen (edited 02-12-2004).]

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                      • #12
                        Now, THIS I remember. There was a long discussion about this here, maybe a year ago.

                        Somebody here makes these nozzles professionally (oh wait, maybe it's you?) and had an oddball thread. It turned out that the firefighting industry had standardized this oddball thread amongst themselves, decades ago. Something like that.

                        Do a search?

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                        • #13
                          This is a part that no normal person would ever adapt into, so I foolishly assumed that they were standard. There would be no point in using a proprietary thread, and there is enough room to use a bigger or smaller, and more common thread. Go figure.

                          Dr. Rob, I don't remember/can't find that thread using the search engine. I do indeed make a firefighting tool, but I only use NORMAL threads! I did find a helpful post on unusual threads, perhaps that is the one you remembered.

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                          • #14
                            Joel
                            Is this a part for the Smoke Jumpers in California ?
                            Dr Rob is corrrect, they have some special threads used on their equipment for two reasons. First is to control quality...No xxx hardware stores parts wanted !
                            Second is to keep it within the "industries "control. If you contact someone in the fire industry, they can give you the specs I believe.
                            Lastly, as long as you stick to the Machinery's Handbook, you can make any size thread following the general rules. The only missing part is the class of fit, which yur customer should provide.

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