What industry or products use larger diameter 18-24 tpi threads?
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  1. #1
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    Default What industry or products use larger diameter 18-24 tpi threads?

    See pictures of thread gauges we got, which were mixed in with other unrelated stuff, the origin of which is unknown to me. Maybe if I study the cal tags I can figure it out. But meanwhile please tell me what advantage is presented by such fine threads on “large” shafts, capscrews, or whatever. I’m not sure I’ve ever seen a large capscrew with such fine threads.

    c0912944-3db9-4c00-9152-4fe7cb564114.jpg855f76e1-3260-4ad2-9bc9-617ac51d2c0c.jpg

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    First, your pics are so small I can't read any of the engravings on the gages.

    Large, fine threads may be uncommon but are not necessarily unusual. Machinery's handbook has specs for
    3-1/4 x 20 threads; 1-5/8 threads go to 28 pitch. No ideas on any specific industries but extra fine threads do
    show up on larger diameters from time to time.,,

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    obviously instrumentation and optical lens assemblies of thin walled thin walled tubing and or thin castings dont need or require coarser threads.
    .
    also pipe fittings like bsp threads relying on gaskets or orings do not require coarse threads

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    Quote Originally Posted by DMF_TomB View Post
    obviously instrumentation and optical lens assemblies of thin walled thin walled tubing and or thin castings dont need or require coarser threads.
    .
    also pipe fittings like bsp threads relying on gaskets or orings do not require coarse threads
    What he said + finer threads require less torque to achieve the same clamping pressure.

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    Camera shutters have external threads of M61 with 0,75mm pitch (roughly 32tpi).
    That's the highest I found with a quick search in my datasheets.
    There are other larger shutters.

    - Leigh

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    Some electrical cannon-type plugs have a similarly fine pitch locking ring.

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    Bicycles.
    1 3/8" x 24 tpi for the gear cluster on the back wheel for example.

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    Mobile home axles have biggish fine threads on the big castle nuts that holds the hubs on.

    metalmagpie

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    Quote Originally Posted by Rudd View Post
    Bicycles.
    1 3/8" x 24 tpi for the gear cluster on the back wheel for example.
    For some freewheels, yup. Also, for bottom brackets (the thing that holds the crank and front chainring).
    British/ISO is 1.370 x 24, or 1.375 x 24.
    To see just how many "Standards" there are, check out Sheldon Brown's Threaded Bicycle Bicycle Bottom Bracket Crib Sheet
    You will see that the "Italian" standard for bottom brackets is/was 36mm x 24 tpi.

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    I was guessing there were 1.875 plethoras of std. bicycle threads.
    All I have worked on is the rear axles for the local pedicab company. The cabs are made in Asia, and the axles either break or wallow out the key seat. I've about worked myself out of a job on that one, the axles I make don't F up.

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    Quote Originally Posted by Cannonmn View Post
    See pictures of thread gauges we got, which were mixed in with other unrelated stuff, the origin of which is unknown to me. Maybe if I study the cal tags I can figure it out. But meanwhile please tell me what advantage is presented by such fine threads on “large” shafts, capscrews, or whatever. I’m not sure I’ve ever seen a large capscrew with such fine threads.

    c0912944-3db9-4c00-9152-4fe7cb564114.jpg855f76e1-3260-4ad2-9bc9-617ac51d2c0c.jpg
    Fine threads have two main advantages.

    1. More resistant to loosening from vibration is probably the most relevant one.

    2. A fine thread can be "stronger" than a course thread.

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    Threads holding bearings onto a shaft or into a bore are often finer threads then expected. From info here I guess to generate more locking force with less then ideal wrench ability. Such as a hook wrench or pin wrench down inside some akward place.
    Bill D.

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    Quote Originally Posted by Bill D View Post
    Threads holding bearings onto a shaft or into a bore are often finer threads then expected. From info here I guess to generate more locking force with less then ideal wrench ability. Such as a hook wrench or pin wrench down inside some akward place.
    Bill D.
    Bearing nuts are locked with a lock tab. They don't need to be all that tight, just not come loose.

    The energy industry is pretty much standard on 4, 6,8,and 12 TPI. I would look at bearing lock nut threads for a match. These are not really large. We deal with studs up to 6" and usually 8 TPI. Stuff over about 2 1/2 is usually stretched by hydraulics or thermally.
    B

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    Guys thanks for share such knowledge with us.

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    Castle nuts on hydraulic and conventional press column posts. I made a post one time, was 4"-24 I think. Hell I forget, I do remember it was super fine.

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    Quote Originally Posted by tdmidget View Post
    Bearing nuts are locked with a lock tab. They don't need to be all that tight, just not come loose.
    Depends on the bearing. A lot of back to back angular contact ballscrew support bearings are preloaded by the locknut. You torque it to spec and then lock it down with a setscrew.

    I think the big advantage of fine threads for bearing locknuts is that the nut can be thinner. You also see some weird threads, like 1.5625-18

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    We have a part that is a "cap" that holds a bearing with a 2-1/4 - 24 thread
    I believe the fine threads were chosen(30 years ago) to facilitate less movement within the mating piece.
    The bad part about fine threads on larger parts(actually on any size part) they're easier to cross thread evan with a line up stub at the start of the thread.

    and another part we make has a 1-9/16 -24, chosen to prevent customer from using off the shelf fasteners

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    Quote Originally Posted by Cannonmn View Post
    See pictures of thread gauges we got, which were mixed in with other unrelated stuff, the origin of which is unknown to me. Maybe if I study the cal tags I can figure it out. But meanwhile please tell me what advantage is presented by such fine threads on “large” shafts, capscrews, or whatever. I’m not sure I’ve ever seen a large capscrew with such fine threads.
    Calibration tags on thread gages tell me these used to belong to aerospace. We use large diameter fine threads on stuff all the time. None of the other uses mentioned would likely require a yearly calibrated gage.

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    thread pitch for screws and tapped threads was determined based on coarse enough thread pitch screw would break rather than thread strip out. long ago 1/2-12 and 1/2-13 threads were not standardized. and of course 55 degree threads and 60 degree threads were still being debated.
    .
    when machine components are not solid like a pipe fittings or a bearing tapered sleeve with lock nut threads you do not require a coarse thread to have enough strength for the application
    .
    some threads even when metric are a thread pitch not commonly used often cause machine designer wants it to be a special part


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