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New one on me! 27tpi

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  • New one on me! 27tpi

    Trying to do a browny point job for the misses - I thoght it would be simple unscrew the broken plastic bulb holder on her candle stick lamps and screw on the new brass ones. First job unscrew the old fitting but no luck after heaving and straining, so removed to workshop.
    Put lamp stem in vice(after wrapping in rag) unscrewed using strap wrench , boy was that sucker on tight. Finally got it all apart, cleaned gluse from threaded portion of rod that held the lamp fitting to the lamp. Offered up the new brass fitting and low and behold threads dont match.
    So try to measure thread on rod but no matter which gauge I tried no luck.
    It is somewhere about 28 tpi, so resorted to counting the threads over an inch this gave the thread as 27 tpi which I had never heard of did a quick search on fleabay and found several at somewhat extortionate prices but found one at £8 so I have brought it . Another tool for the pile, why do they make these odd threads. I'm not sure I can cut a 1/2" od 27 tpi thread on the lathe so I may end up soldering the adaptor in the holder.
    I think I should have just gone and bought an adaptor but thats no fun is it!

    I have tools I don't know how to use!!

  • #2
    27 TPI is standard for 1/16" and 1/8" pipe. Any thread count can turn up on anything, there is only a "standard" for fasteners and common items such as pipe threads and such. Many industries have their own standards, and manufacturers have their own proprietary threads.

    1" to 2" pipe threads are 11-1/2 TPI. A good QC gearbox will cut 11-1/2 & 27 TPI, but those counts do not appear on many. It is another thing to look for when choosing a lathe.
    Jim H.


    • #3
      It is frequently possible, on lathes with a QC that does not include 27 tpi, to put a different gear on the end of the leadscrew and get 27tpi that way. For example, I can do that on my 10K although I've forgotten what the gear needs to be.
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie


      • #4
        Most lamp parts, sockets, hickeys, adapters, etc. that I've encountered use pipe threads, either straight or tapered. Both 1/16" and 1/8" pipe threads are 27 TPI. Taps and dies are readily available for both straight and tapered

        This seems a bit odd at first, but perhaps this usage is a carry over from the old days of gas lights.


        • #5
          And even if the threads are NOT tapered pipe threads. Straight thread adapters are also 27 tpi on lamp parts and other brass work.

          There are some other 27tpi threads as well, I forget on just what.

          It gets left off most QC boxes, so all of us with change gears get to laugh at you..... it is almost always a standard setting with change gears.

          Keep eye on ball.
          Hashim Khan


          • #6
            5/16-27 for shotgun cleaning rod brushes, mops, etc.

            Montezuma, IA
            David Kaiser
            “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
            ― Robert A. Heinlein