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Another Tap Question

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  • Another Tap Question

    I found this tap in a batch of old ones I got at an auction. It's a 9/16-12 but the odd thing about it is the size stamp (9/16) is followed by "1/32" before the thread count. What does the 1/32 mean?

  • #2
    I think it is for tapping a 1/32" oversize hole, so that after the part is heat treated it ends up the correct size. Gary P. Hansen
    In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.


    • #3
      Yikes! .031+" oversize is pretty big even for heat treating. Now that you mention it, I wonder if this could be thread depth?

      Not that- I just measured the thread depth (approximate), it's over .031.


      • #4
        Measure the tap OD and see what you get.
        I just need one more tool,just one!


        • #5
          Pure guess, but it may be for a tapered thread (pipe thread) the slope being one in thirty two.
          Murphy was an optimist


          • #6
            Well, it could be . . .

            Ken --

            About a century ago the Aermotor Windmill Company started tapping their windwheel hubs 1/32 inch oversize, and they are still doing so today despite moving their manufacturing plant from Chicago to Oklahoma, stopping domestic production in favor of outsourcing to Argentina, building a new plant in Arkansas, and then moving to San Angelo, Texas. The original reason for the oversize hub holes seems to be lost to history, but some of today's experts think it was a "proprietary parts" scam, while others suspect that the oversizing was to provide clearance for a build-up of hot-dip galvanizing on the male threads.

            Your tap isn't for the Aermotor hubs, though, because Aermotor's (9/16 + 1/32) tap is specified as "19/32-13 NS".

            If you should happen to need an Aermotor tap, though, Bur**** & Bur**** out in El Paso will sell you one. http://www.bur****andbur****.com/Cat...G/G-01%20W.pdf



            • #7
              Well I'll be. I measured across the threads as best I could with the Ching-Chang calipers and got .5945". 9/16 is .5625 so it does appear to be 1/32 oversize.

              Dang Gary, sorry for doubting you.

              Other than the starting portion, the threads aren't tappered.

              No Aermotor John. I've been using it to press bushings out of Model T spindles though.
              Last edited by CCWKen; 08-30-2006, 12:23 AM.


              • #8
                Interesting stuff. At first I figured it was a matter of bad labeling, like my pair of taps, below, both clearly marked 1/4-20:


                Frank Ford


                • #9
                  Dormers used to have a place just round the corner from me about 20 years ago.
                  We used to fish bits out there scrap skip at night but gave it up when we realised why they were in there

                  Marked wrong, undersized, oversize, incorrectly hardened etc but I did still get the odd gem out.

                  They closed down here and moved to Sweden or somewhere.

                  At that time I was involved in trucks and we used to handle the trucks from the biggest 7 of the local scrap merchants, most were interrelated by marriage and it was a bit of a closed shop but once you were in with one you were in with all.

                  Many time we had to go out to the yards to repair trucks and grabs so we had full run, not like nowadays with H&S.
                  There was a lot of good stuff coming into the yards at this time as CNC's were replacing manual machines and the downsizing was starting.

                  Just a bit of history here,

                  During the 80's we had a large miners strike here that was aimed at crippling the country to get them more power.
                  The PM at the time, Margaret Thatcher, decided it wasn't to be and without getting political, just an insight to what happened next, basically crushed the unions here.

                  During this period industry was forced to go on a 3 day week to save power, some were exempt, like oil delivery's and truck garages who had an old oil truck parked in supposedly being worked on
                  What happened during this 3 day week is that management were forced to revue operations and get around this.
                  The result was that many got as much out in 3 day as they were doing in 5.
                  When the strike ended many places shed jobs, staff and equipment as they realised it wasn't needed, again not being political but the unions did many of the working class a disservice over this.

                  During this time whole sub contract shops came thru the scrap yards, that many it was impossible to sort and process and much just went into the crusher.

                  It was during this time I collected a lot of my equipment, often for free on smaller parts or pence on larger ones.
                  I still keep friendly with two of the scrappies but most have disappeared, retired and multi nationals are now running the show.

                  Sorry for the boring history lesson.


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


                  • #10
                    Actually the three day week was in the 70's under ted heath not margaret thatcher she did have a problem with the miners in the eighties with arthur scargill terrible problems with strikes then but no three day week then sorry facts a bit twangled sur geon that's sir john Alistair
                    Please excuse my typing as I have a form of parkinsons disease


                    • #11
                      Who asked you ?

                      Yes you are right [ God it hurts to say that - ouch ]
                      The point I was making was that 3 day week started the decline as they realised how much dead wood they were carrying and downsized accordingly.
                      That together with improved technology saw a lot of older equipment go thru the shears and crushers.


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


                      • #12
                        Oversized taps

                        GH11 is the designation stamped on taps that come .005 oversized. This is used prior to heat treatment on die steels so that the bolts will go in after the heat treated steels move around and warp shrink and do whatever they want to.


                        • #13
                          I love machining history and thanks. I thought the unions were stronger than that over there? What's up with the labour party? I'll have to read up on that.


                          • #14
                            Originally posted by Millman
                            What's up with the labour party? I'll have to read up on that.