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Identifying Internal threads

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Identifying Internal threads

Home › Forums › Workshop Techniques › Identifying Internal threads

Viewing 8 posts - 1 through 8 (of 8 total)
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  • 12 January 2021 at 17:11 #519360
    Vic
    Participant
      @vic

      Anyone got any tips on how I might Identify an internal thread on a machine? Its not metric and I don’t have any imperial bolts of a likely diameter to try. I’m not in the workshop at the moment but I think it’s likely 5/16 or 3/8 something or other! I’ve got some thread pitch gauges but not too easy to use on internal threads.

      12 January 2021 at 17:11 #16235
      Vic
      Participant
        @vic
        12 January 2021 at 17:13 #519361
        Michael Gilligan
        Participant
          @michaelgilligan61133

          Screw a suitable diameter of wood or plastic into it

          … unscrew, and measure the pitch of the male thread

          MichaelG.

          12 January 2021 at 17:14 #519362
          Pete.
          Participant
            @pete-2

            Use some polymorph, it's cheap, and reusable

            12 January 2021 at 17:28 #519367
            Tony Pratt 1
            Participant
              @tonypratt1

              Okay not easy with your limited 'equipment',what m/c is it & how do you know it's not metric? Give us the manufacturers name that will be a good clue.

              Tony

              12 January 2021 at 17:58 #519378
              Vic
              Participant
                @vic

                Update. I’ve seen reference to the size in the manual for a later model so I have a staring point now. Apparently it’s UNC.

                12 January 2021 at 18:20 #519387
                Tim Stevens
                Participant
                  @timstevens64731

                  I have had success using a simple wooden toothpick. Break off the sharp end, and slide the pick around the thread while keeping it in line with the axis, using pressure from a finger (etc). This should result in a series of grooves or dirty lines (or both) along the pick, so you can measure how many fit to an inch or to 25mm. Then a moment's calculation should reveal the threads-per-inch, or the pitch in mm.

                  Cheers, Tim

                  12 January 2021 at 19:09 #519401
                  David Marks 2
                  Participant
                    @davidmarks2

                    If you have a set of Letter series drills you should be able to get a good idea of the core diameter of the thread by inserting the shank of the drill into the hole. Regarding the thread profile and TPI, a small amount of car body filler placed into about 30 – 40% of the thread works. Due to the thread shape it lifts out very easily.

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