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HSM May/June Article: The Odd Screw

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  • HSM May/June Article: The Odd Screw

    I was reading this article by Paul Holm and started wondering about non-standard screw sizes and how common they might be. The problem that formed the basis of the article was a Craftsman tool holder that used a 3/8"-18 screw to secure the tool. Why would they do that.

    I have a few tool holders that haven't been used for some years now since I made my quick change holder so I broke them out and checked them out. All are for 1/4" tool bits. Here's what I found:

    Armstrong, U.S.A., No 0-R: 3/8"-18 screw

    Armstrong, U.S.A., No 0-S: 3/8"-18 screw

    J. H. Williams, U.S.A., No 0-L: 3/8"-18 screw

    No name, import, no number: 5/16"-18 screw

    All the US made holders have the 3/8"-18 screw and the import has a 5/16"-18 TPI screw. Someone likes 18 TPI. Apparently the "Odd Screw" is not that odd after all. Craftsman isn't the only one who used it. And yes, I know Craftsman is just another manufacturer with their name on it. They probably just said to make them the same as the manufacturer's own line.

    Armstrong seems to still be in the business as I saw their holders listed in at least one catalog. I can only wonder if they still use the same screw and if they could supply replacements. Their holders are $100+ so expecting them to supply replacement parts would not be out of the question. But at what price? Perhaps the author has it right, make your own.
    Paul A.
    SE Texas

    Make it fit.
    You can't win and there IS a penalty for trying!

  • #2
    In the case of the toolholders, it is probably a legacy issue. Toolholders date back to the beginning of time when there were no real standards, and 18TPI was probably not uncommon. Another thread that appears frequently is 12TPI, 1/2"-12 being frequently used on older machinery.

    It was not until WWII that standards were created in the interests of interchangeability. This left some manufacturers of specialized equipment with the quandary of what to do with their product, continue the now non-standard thread and make replacements for all existing parts difficult or continue with the odd thread. Apparently Armstrong etal decided on the latter and 18TPI is the standard thread for rocker toolholders.
    Jim H.

    Comment


    • #3
      5/16-18 isn't an odd thread...I use it almost every day.

      Comment


      • #4
        Originally posted by JCHannum
        In the case of the toolholders, it is probably a legacy issue. Toolholders date back to the beginning of time when there were no real standards, and 18TPI was probably not uncommon. Another thread that appears frequently is 12TPI, 1/2"-12 being frequently used on older machinery.
        1/2" x 12 was the first real standard, it British Standard Whitworth and was in use before any other standards were dreamed up.
        It's NEVER been withdrawn and is still current today and used all over the world.
        The Taiwanese use it and later the Chinese and Indians copied it that's why you come across this on mill drills etc and call it a bastard thread when in fact only the Americans made their 1/2" standard 13 instead of the existing 12.

        Why ?? no one knows but as is common it was to tie in to certain manufactures and say "We invented this "

        Rather ironic that in 1841 when Whitworth come up with his standards of 55 degrees and rounded tops he had enough knowledge to know it was the best thread design.
        Twenty odd years later in the 1860's when Sellers can up with what is now the Unified series he did it for ease of use with 60 degree angle and flat crests.

        Modern tests on both thread forms have determined that the Whitworth thread is stronger. I feel that Whitworth is one of the most under rated engineers we had.
        It's well worth reading the book Sir Joseph Whitworth to see how badly treated he was.

        http://www.amazon.co.uk/Sir-Joseph-W.../dp/0750912111

        .
        .

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



        Comment


        • #5
          Originally posted by John Stevenson
          1/2" x 12 was the first real standard, it British Standard Whitworth and was in use before any other standards were dreamed up.
          It's NEVER been withdrawn and is still current today and used all over the world.
          The Taiwanese use it and later the Chinese and Indians copied it that's why you come across this on mill drills etc and call it a bastard thread when in fact only the Americans made their 1/2" standard 13 instead of the existing 12.
          60° UNC and 55° Whitworth nuts and bolts are often used one with the other, except for 1/2" of course, in countries where they occur together.

          Out of curiosity, are the Taiwanese et al threads usually 55° Whitworth form or 60° form?

          Comment


          • #6
            Isn't 12tpi the standard fine thread for most everything 1" diameter and above? I have a 1x12 as well as a 2 1/4 x 12. I know 9/16x12 is common as well.
            James Kilroy

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            • #7
              1/2-12? That is much better than 12/13!

              Comment


              • #8
                " Sir Joseph Whitworth (Hardcover)
                by Norman Atkinson (Author) "

                Har! Go Norm!

                Comment


                • #9
                  No it's not by Norman because you can understand what's written.

                  .
                  .

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



                  Comment


                  • #10
                    Originally posted by John Stevenson
                    No it's not by Norman because you can understand what's written.

                    .
                    LOL!!!! Thats your second best line in 2 days John!!!
                    Ernie (VE7ERN)

                    May the wind be always at your back

                    Comment


                    • #11
                      I think the entire metric series is an odd bod thread..Every bloody country uses a different bolt head size and thread pitch/bolt diameter..

                      Whitworth FTW..
                      Precision takes time.

                      Comment


                      • #12
                        odd thread of the week - 3/8 x 19 BSP,
                        aaarrrgggghhhhh 19 tpi???????

                        lucky i had the right tap and die.

                        Comment


                        • #13
                          Originally posted by thistle
                          odd thread of the week - 3/8 x 19 BSP,
                          aaarrrgggghhhhh 19 tpi???????

                          lucky i had the right tap and die.

                          What is odd about 3/8 X 19 BSP it is a standard thread better then 2"X11 1/2 NPT..
                          Precision takes time.

                          Comment


                          • #14
                            The only fault I see with the whole Whitworth thread thing is the way the hex head sizes were set. (needing goofy-a$$ed wrench (spanner) sizes)

                            It's the reason I sold my 1959 Land Rover. That bastard-vehicle had multiple kinds of fasteners all over it.

                            BTW, what Old Blighty joker thought that King Dick was a good name for tools?

                            Comment


                            • #15
                              Wrong

                              Originally posted by Jeffw5555
                              The only fault I see with the whole Whitworth thread thing is the way the hex head sizes were set. (needing goofy-a$$ed wrench (spanner) sizes)

                              It's the reason I sold my 1959 Land Rover. That bastard-vehicle had multiple kinds of fasteners all over it.

                              BTW, what Old Blighty joker thought that King Dick was a good name for tools?
                              Wrong, as Whitworth was the first standard thread all head combinations after that are the goofy ones

                              Comment

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