32 TPI-series threads - What are they used on?
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  1. #1
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    Gents,

    Recently got a big bag of about 40 asst'd taps thrown in as a "boot" on a deal for some other machinist's tools. Sorting through them, I found some oddities: 1/4-32, 5/16-32, and 3/8-32. All are marked "NS", meaning that the threads have the National Standard form.

    Machinery's Handbook lists these sizes, but of course they are not NC or NF. I don't think they are NEF, either, at least not all of them.

    What sort of work are they used for?

    There were two other oddballs in the bag - an NPS and a "lefty". All-in-all, a nice addition to my little drawer of "Taps I'll probably never use, but which might be very useful if I ever need them" :rolleyes:

    John Ruth

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    Bearing lock nuts. NS could also mean National Special.

    John

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    I have always heard NS refer to National Special also
    Jim

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    Electronic potentiometer (variable resistors) panel moung threads. You got a set of taps to make the three sizes of rentntion nuts for them.

  5. #5
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    I think the 3/8-32 is also the strange size that electric lamp mfgs use for the OD of the tubing that holds the lamp socket, harps, etc.

  6. #6
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    I've seen -32s used in a lot of places. I suspect they are a frequent choice for fine, nonstandard threads because 32 is a multiple of the popular lead screw sizes of 8 TPI and 4 TPI.

    3/8-32 was the only size that pots (variable resistors) came in for many years. It allows a 1/4" shaft to sit in a 3/8" bushing with outside threads and enough metal left for gorilla tightening. Then they started going metric and down sizeing. But they still use thread pitches in that area.

    Many other uses for extra fine threads, usually for similar reasons. A 1" or 25mm diameter filter for a camera lens would have a considerablly smaller optical diameter if UNC threads were used. 3/4" or so. They can also be used where a fine adjustment screw is desired and the size needs to be larger than a #10.

    Ditto on the National Special abbreviation.

    Paul A.

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    Glow plugs for model engines are 1/4-32
    Pete

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    I think Holley carburator jets are 5/16-32. If I remember, thermalcouples used on furnaces and hot water tanks are 11/32-32, 2-start thread.
    --Doozer

  9. #9
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    I think the 3/8-32 is also the strange size that electric lamp mfgs use for the OD of the tubing that holds the lamp socket, harps, etc.
    Actually, Ferrous, those are typically 1/8-27 straight pipe threads. The major diameter is around 0.400.

  10. #10
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    Those are all standard electronics equipment
    threads. For example, most miniature toggle
    switches are 1/4-32.

    And BNC connectors are threaded 3/8-32, those
    are very common.

    Jim

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    These taps also come in quite handy when you want to piss off a customer. Tap an unspecified tapped hole with one of these specials and let them figure out where to get the screws.

    Also if you make the mating parts, they wind up coming back to you for replacement parts.

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    Sim wrote: "These taps also come in quite handy when you want to piss off a customer. Tap an unspecified tapped hole with one of these specials and let them figure out where to get the screws.

    Also if you make the mating parts, they wind up coming back to you for replacement parts. "

    Back a few years I had customer prints with the designation "thread pitch machinist's choice". Part was similar to a camera lens mount.

    This was a large diameter thread that needed to be milled because of part size, I just happened to have 28tpi milling inserts in the holder so used that. Parts worked fine, but I mentioned this was a bastard thread and to be on the safe side they should have me make a set of crude "go/no-go" gages and establish written pitch diameter specs just in case. Nope, didn't want the spend the few bucks it would have cost.

    This customer was basically very cheap. Of course they found an offshore source for the parts. They mistakenly specified the thread as a 24tpi which was a common pitch in their industry.

    OOPS, they ended up with a ton of parts with the wrong thread. Hard not to smirk a little when this type customer comes crawling back asking for help in trying to figure out why their new parts don't work.

  13. #13
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    John,
    If you do not want them, let me know I will take all the 32 thread taps in the bag. I use them for alot of my model aviation products I produce. Still looking for a 17/32-32 tap & die for one particular work piece, custom size very hard to find short of having it custom made and that may happen so enough.

    Scott

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    In the United Kingdom there are two series of something called Model Engineers taps and dies.
    Obviously, they are small diameters and for models. They are 32TPI and 40TPI.

    Importantly, if you have some 40's you can get instant thousands of an inch for many tools.

    Regarding the " Lefty". This suggests that these were the property of a "Live Steamer" at one time.

    Hope this proves of some help.

    Norman

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    Got a copy of one of the Synoptic Gospels.

    Listed are 16 sizes in 32 and 40TPI's
    and 7 in 26TPI and range from 1/8 to 5/8ths

    The left hand threads are 3/16 and 1/4 BSW.
    These are listed for Reverser Screws on steam locos.

    You would appear to have a very expensive collection of goodies
    N

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    We use 3/8-32 & 5/8-32 threads at work every day in our product line, primarily on thin wall tubes. We need the shallow depth of thread, as well as a fine thread to keep things from coming undone.
    Bob

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    5/16-32 is the thread for the cap of a tire valve stem

  18. #18
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    Oh yeah, you'll NEVER use those. You better box 'em up and send them to me. I've gotta rack just for them.

  19. #19
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    Norman said,

    "Importantly, if you have some 40's you can get instant thousands of an inch for many tools."

    Yup, I bought a 1/4-40 tap some years ago when I was making a knife edge tester for telescope mirrors. I turned the screws from 1/4" brass rod on the lathe. Instant, inexpensive micrometer adjustment.

    Great addition to my toolbox.

    Paul A.

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    1/4-32, 5/16-32, 3/8-32 are listed as NEF series standard threads in my Federal Handbook H-28. Here is info from the handbook: "The American National Extra-Fine-Thread Series is intended for special uses where (1) thin walled material is to be threaded, (2) thread depth of nuts clearing ferrules, coupling flanges,etc., must be held to a minimum, and (3) a maximum practicable number of threads within a given thread length. This thread series is the same as the SAE extra-fine-thread series, but it includes additional sizes." The threads listed in the series run from 1/4-32 to 2"-16. (example, 1/2-28, 3/4-20). A 3/4-24 thread would not be a standard size, but a special size.
    The H-28 Handbook has been replaced by a Mil-Standard or Spec.I have a copy somewhere. I believe it includes the same info as the H28 Handbook.
    Sy


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