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Bastard sized flare nuts

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  • Brakes: Bastard sized flare nuts

    I wanted to pass on something I found out the hard way on some of the inverted stainless flare fittings on a brake conversion on my '54 Hudson. I purchased the distribution block from Speedway and it came with two short stainless lines to connect it to the MC. The lines were already flared with stainless fittings. When I connected it I only finger tightened the lines so I could adjust them once it was mounted and in place. This is not as easy as I thought as the fittings on the MC I used were on the right side toward the engine and the brake light switch was in between the two connectors on the right side of the block. Well, as I tried to tighten them I could not get my 3/8" tubing wrench or even open wrench to fit on the nuts! I thought what the hey here!! I then realized that the lines were supposedly 3/16" but the fittings were METRIC! The nuts were 10mm, luckily I had a 10mm tubing wrench, which I had never used for all of probably 30 years. Anyway I went on line and found that others had had issues with other supposedly English sized tubing nuts that turned out to be metric, but were advertised as 3/8 x 24 for 3/16" tubing, also some found oversized ones at 12mm. So I am guessing these came from China and are bastard mix of English tubing with metric sized nuts on the outside and English 3/8-24 threads. So be aware this may happen to you!
    Dan White
    64 R1 GT
    64 R2 GT
    58 C Cab
    57 Broadmoor (Marvin)

  • #2
    I have found that with recently purchased nuts and bolts , The threads are 1/4x20 but the the heads are 10mm , Bastards ! They were returned ,Ed


    • #3
      Does that mean they fit me? Asking for a friend.
      Bez Auto Alchemy

      "Don't believe every internet quote" Abe Lincoln


      • #4
        I had a similar experience with new, replacement wheel cylinders. Everything installed correctly, I went to bleed the brakes and none of my SAE wrenches fit the bleeder screws! Turned out they were 10 MM. UGH!
        Howard - Los Angeles chapter SDC
        '53 Commander Starliner (Finally running and driving, but still in process)
        '56 Golden Hawk (3 speed/overdrive, Power steering - Running, but not yet driving)
        '62 GT Hawk (4 speed, A/C, Power steering - running and DRIVING!)


        • #5
          Had a similar experience in the Model A Ford world. I ordered a new reproduction rumble seat step bracket. The fasteners were metric. Old Henry would probably roll over in his grave.
          Dan Peterson
          Montpelier, VT
          1960 Lark V-8 Convertible
          1960 Lark V-8 Convertible (parts car)


          • #6
            Piling on: Same thing with some newly-purchased of 45-degree zerk fittings. Threads were correct, but the little hex heads were metric. Obviously, whomever wrote the spec forgot to tell the Chinese to use US standard sizes on both ends. Neither the Japanese nor the Taiwanese used to make those kinds of mistakes.

            Edit: after further thought, maybe they're not mistakes. Any working mechanic today would probably have metric tools readily at hand, and have to get up and go to his tool box for an SAE wrench. But the threads on an old car can't be changed, so a part that fits an SAE thread but has a metric hex head may not be all that bad of an idea.
            Last edited by Skip Lackie; 09-25-2020, 12:24 PM.
            Skip Lackie


            • #7
              Many metric and imperial are readily interchangeable, 5/16 = 8mm, 7/16 = 11mm, 1/2 = 13mm,
              9/16 =14mm, 5/8 = 16mm, 3/4 = 19mm, 13/16 = 21mm, 7/8 = 22mm.

              The 10, 12, 15, 17, 18, 20 mm only fit themselves. Some only fit one way. When you work with both sets you get to remember which fits what. Any way you want to slice it it is a PITA. I have two tool cribs and they are constantly mixed up and require regular sorting, specially when my 18 year old grandson uses them.


              • #8
                This is very common these days. I've noticed it becoming more and more common over the last 20 years or so. The ones that bug me are the fittings with the correct SAE threads but with a hex that fits neither a SAE wrench or metric wrench.