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How often do you run into oddball thread sizes?

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  • How often do you run into oddball thread sizes?

    Tinkering at some amateur gunsmithing I've often run across odd ball thread sizes. Just had it happen today in fact. Working on an old Steven's Little Scout boys single shot. The take down screw was bent and holding the barrel back from properly head spacing to the pivoting block.

    Now this is a full on restoration since the gun was originally cancer ridden on many levels. It had gone WELL past the concept of "patina". Even so I don't take on a full restoration lightly. It's got to be pretty bad. But this one sure did qualify.

    Anyway I figured "no biggie, I'll make a new one or cut off the threaded pin and make a new one from a grade 8 machine screw..... NOT! The threaded portion is either #10 or it's 3/16". And the thread pitch is really close to 28 but also fits a 27 TPI gauge pretty well. Yep, not 24 or 32 TPI. So I had to make up an aluminium holder for the thread and carefully knock it back into shape.

    It's not the first time I've been tinkering with some of my firearms and run into oddball sizes. It seems like the early part of the 20th might have had standards but that companies were slow in falling into line. I've run into other odd ball sizes on stuff dating from up to around 1930.

    Of course there was also my time with that Myford I had. But those were only weird sizes because it had been sent forth from its country of origin. Oh... and the Austin Healey Sprite I had for a while.....

    So who's run into some seriously obsolete thread sizes and what was it on?
    Chilliwack BC, Canada

  • #2
    all the time.....or I make up my own lol. Just did a 1 5/16 x 20 for example, it just worked out to be the right size for the project.

    I remember as a teenager buying an ancient wood lathe at a farm auction. Wood bed with steel covers, all ornamentally painted -like the pinstriping you see on an old wood threshing machine. Anyway, there were two big bolts on one one of the head stock bearing caps, and each would only fit is screw and they each fit smooth as silk. how odd ball a thread is that? different on the same bloody machine
    .

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    • #3
      I once had to make a 3.750 OD x .875 Pitch double start Brown & Sharpe thread for a big assed winch.

      http://neme-s.org/BS_Thread_Tool/BS_Thread_Tool.htm

      Errol Groff
      Last edited by Errol Groff; 12-17-2016, 09:36 PM.
      Errol Groff

      New England Model Engineering Society
      http://neme-s.org/

      YouTube channel: http://www.youtube.com/user/GroffErrol?feature=mhee

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      • #4
        Some of the odd-ball thread sizes you see on older guns and machines are related to the dysfunctional trait that many engineers suffer from: the Not Invented Here Syndrome. In some cases, it's from gun screws that were developed before standardization and the factory found it was easier to keep making the same size on newer versions of the same rifle rather than have to stock two or more sizes for guns of the same design. In other cases, it kept you as a captive customer...no going to the local hardware store and getting a "standard" size screw for that breechblock to pivot on!
        David Kaiser
        “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
        ― Robert A. Heinlein

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        • #5
          Originally posted by Mcgyver View Post
          all the time.....or I make up my own lol. Just did a 1 5/16 x 20 for example, it just worked out to be the right size for the project.

          I remember as a teenager buying an ancient wood lathe at a farm auction. Wood bed with steel covers, all ornamentally painted -like the pinstriping you see on an old wood threshing machine. Anyway, there were two big bolts on one one of the head stock bearing caps, and each would only fit is screw and they each fit smooth as silk. how odd ball a thread is that? different on the same bloody machine

          I remember reading about a guy that worked at a machine shop, everyone there called him Snowflake.
          No two parts the same.
          Home, down in the valley behind the Red Angus
          Bad Decisions Make Good Stories​

          Location: British Columbia

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          • #6
            Originally posted by Willy View Post
            I remember reading about a guy that worked at a machine shop, everyone there called him Snowflake.
            No two parts the same.
            I darn near spit out my beer and pizza at that one ! ! ! !

            The standing joke among one of the shooting groups I'm in is that anyone having a bad day is named "Lightning". And it's not for their speed... It's because lightning never strikes in the same place twice....

            Mcguyver, you reminded me of the time I needed an adjustable plug to fit a 1/2" bore. It was for a paintball gun project at the time and I was stuck with the 1/2 inch ID size to fit a rare earth magnet. It was for an "anti bust" bolt if it matters. So I made my own tap AND then a die for a .55-32 thread. I've still got these two items kicking around here somewhere... just in case you know....

            38-Cal, I suspect there's a LOT of truth in that. And likely some pressure to use tooling already paid for and sitting in the tool room. So to be fair it might not ALWAYS be the engineer's fault. They had bean counters back then too. Just smarter managers didn't listen to them exculisively.
            Chilliwack BC, Canada

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            • #7
              Odd ball threads? No need to look very far if you have older B&S or Starrett tools. Or current Starrett, for that matter (0.110-52? Really?).

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              • #8
                I'm occasionally guilty too.. make it fit. But every time one of us does that someone down the road will have to do the same to fix it.

                Not just me. Rotary indexer - the so-called 1-8 spindle was not standard... I made it so. B&S grinder - wheel hub thread not standard either.
                Last edited by lakeside53; 12-17-2016, 09:46 PM.

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                • #9
                  Not oddball at all. Thread standardization only came into effect around WWII, and even then there are still variations and standards within specialized fields such as optics.

                  Many earlier manufacturers would standardize on a thread count, say 28TPI, and make all their fasteners that pitch, varying the diameter to suit the use. They also used fractional sizes rather than numbers, and number sizes ran as high as #30. To add to the confusion, in the days before Jo blocks, each manufacturer used his own standards, so one man's 3/32" might not be the same as another's.

                  FWIW, I have a Stevens Crackshot here, the same vintage a type of firearm. The fore end screw is 0.155" shank diameter, thread count is hazy, possibly 27 or 28, but it could be 27-1/2 as they did that too.

                  There are many of these heritage threads still in use today as there is no reason that a specific fastener that screws into a specific part for a specific function need be manufactured to current thread standards.
                  Jim H.

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                  • #10
                    ..... thread count is hazy, possibly 27 or 28, but it could be 27-1/2 as they did that too.....
                    You might have nailed it. The fit of the 27 and 28 TPI gauges were both a tad off. THANKS!

                    The reading I'd done on thread sizes indicated that the history was such that at least the military contracts specified unified thread sizes during the later parts of WW1. But of course this was for military contracts. Civilian commercial companies were not forced into anything and were left to adopt the set standards or not. And governments didn't jump in and force compliance with standards back in those days. So I'm not surprised that odd ball sizes were still around up into WW2 and perhaps even later.

                    Odd that you say you have a Crackshot. My love for these silly boy's single shot rifles started when I was helping a local range owner clean up the storage room. I found an old Crackshot 26 in a box and asked what this was doing there? His response was "... you touched it last...". I rapidly learned the joy of stuffing up to a dozen reloads between the fingers of my off hand and flicking away the empties. I'm up to around 7 or 8 various old early 20th century "boy's" rifles of all sorts now. And I love shooting all of them. But of course as you know they were not designed with the goal of lasting for 100 years. I've got a long list of repairs to perform on the lot of them yet.

                    I found the initials WGP on the stock clearly cut in by some boy with his pocket knife. Not deeply but there and rather "blocky". I asked the guy with the range about these initials and he mentioned a fellow he knew for many years that passed on and the fellow's wife had him liquidate the collection. The Crackshot being one of the last and not really sell-able due to missing a trigger. I made a trigger and got it shooting again. And while I cleaned it up there was simply no way I was going to remove those initials cut in by that young boy who then kept that rifle until the day he passed at the end of what I hope was a long and happy life.
                    Last edited by BCRider; 12-17-2016, 10:07 PM.
                    Chilliwack BC, Canada

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                    • #11
                      Years back I made a paint cup for my HVLP gun. One that came with it was a tad on the tall side, so tall I was really nervous about bumping into freshly laid paint with it due to the contours of what I was spraying at the time.

                      So I go to check the thread size, of course this was AFTER hogging out a pc of 5" 6061 round to about a 40 thou wall and there it was. A .652 OD x 19 TPI....WTF I thought. OD I can handle, but 19 TPI wasn't happening, at least according to the chart supplied with my machine. So, time to work out the equations for my change gears which for me was a job in of itself. Fortunately I'm both standard and metric capable with my change gears, so it was just a matter of doing the trial and error method of plugging in of the available gears in hopes of hitting 19 somewhere along the line. Best I could come up with was 19.047 TPI. Plenty close for a .500 long thread.

                      Guess that's the manufacturers way of making you fork over the big bucks for their cups. Sorry, not me.

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                      • #12
                        Oh come on... I'm pretty sure that the spray gun company wasn't thinking about every customer having a lathe in their back pocket. More likely it was about coming up with their own standard so you didn't buy some other company's cups.... Still, that's a REALLY odd number. 1.333 mm pitch in fact so it's clearly not metric either.
                        Chilliwack BC, Canada

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                        • #13
                          I recently had to make a 14tpi quad-lead thread on a lathe that couldn't go lower than 4tpi.

                          Doc.
                          Doc's Machine. (Probably not what you expect.)

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                          • #14
                            If you want to see odd ball threads look at the Singer sewing machine co. They had plants in NJ, Conn.Germany and England. Each plant had a book of threads and very few was the same as another plants threads. It seemed that each engineer had his own idea of which thread to use.

                            Dave

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                            • #15
                              A .652 OD x 19 TPI....WTF I thought.
                              That would be extremely close to 3/8" BSP thread (0.656 x 19 TPI with 55 degree Whitworth thread form).

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