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  • J Tiers
    replied
    Looks like they just decided that they were going with sizes that did not claim accuracy to a hundredth of a thou..... Didn't they think anyone could measure that difference to better than a tenth of a thou?*

    Oddly, not all the new sizes are bigger. They are almost identical from 8 to 13, and then the new sizes are smaller.

    Unless you have a very old set of taps/dies, the whole thing may not matter at all. And in any case the difference is such that only closer thread classes would really be affected.

    * They were probably right, the hundredth of a thou was a mathematical construct and had no practicality at all.
    Last edited by J Tiers; 04-06-2022, 01:00 AM.

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  • andywander
    replied
    Yeah, the number sizes actually went up to 30.

    And to make it even more confusing, there is an "old" number series, and the "new" or present number series. ASME had a committee working the new sizes from 1908 thru at least 1921

    Click image for larger version

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  • BCRider
    replied
    Originally posted by andywander View Post
    #7-32 (with a nominal OD of 0.154") is listed as a standard screw size in my 1914 Machinery's handbook.
    I've always wondered what happened to the missing sizes in the number size screws. Looks like now we know. Are the others like Albums and #11 in that table as well?

    BC,
    As I understand Stan's original post, he's planning to make new 'upgraded' thumbscrews, so the issue of a sloppy fit wouldn't arise.
    Georgineer, That's what I took it as too. But he's saying that an 8-32 would result in about .01 of slop. So that means the narrower crests of both sides would be doing most of the work. And a good pinch worth of torque might just cause the "chezzium" metal often used on these low cost third hand gizmos to bend over and smear. Depends on how much torque is needed I guess.

    Some of the similar priced items I've seen are not only loose fits on the threads but the threads themselves tend to look like a rabid gerbil gnawed them from the stock. So often the fittings don't thread back and forth all that smoothly. If he's making his own or upgrading the existing to 8-32 I can't help thinking that likely as not upgrading the studs or screws would result in nicer moving thumb nuts overall.

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  • old mart
    replied
    With antique clocks, some will be from before even Whitworth came up with the first standards, so you will have to be prepared to make custom threads.

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  • sjaffe
    replied
    BSW 5/32" 32 TPI is very close, so I will go with that. I used a 8-32 tap on them and only the smallest of shavings resulted. An 8-32 fit fine after that. So thanks for the help, I learned something. I thought there was only Imperial, Metric and BA threads, but now I will need to also consider BSW. I restore antique clocks so have run into several of these various standards.

    Stan

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  • J Tiers
    replied
    Most chinese import products to the US used to use US threads. More recently, the chinese have rebelled, and just use metric fasteners. They don't want to fool with the US stuff any more, take it, or leave it.

    Originally posted by The Metal Butcher View Post

    It is common for cheap threads to be undersized, hence why I suggested that. Measure a piece of 1/2" allthread, it's typically almost 20 thou under. I won't say it is for sure M4x.8, but that size exists on Google.
    The threads are not necessarily undersized. They may be made to a looser class of fit, but the OD difference is due to the flat on the thread crest. Many are cold rolled threads, and you can see the "flat" which is formed as the two ridges of displaced material come together.

    The percent thread may be lower, around 60 to 70%, but the thread size is correct.

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  • Georgineer
    replied
    Originally posted by Paul Alciatore View Post

    I suspect they are mostly made in places like China and Taiwan. So a metric thread is a good bet.
    You might lose your money. I've just been working on a Chinese-made machine which uses Whitworth threads (as well as metric...)

    George

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  • Paul Alciatore
    replied
    Those devices are fairly common in electronic circles. Probably first made by a hobbyist and then picked up by the budget manufacturers. They were available in places like Radio Shack as well as local electronic supply houses. Probably others like DigiKey, Newark, Mouser, etc. I am sure they are still available. I have worked at places that had one but I found them to be of limited use.

    I suspect they are mostly made in places like China and Taiwan. So a metric thread is a good bet. Of course, one which is at the limit of the tolerance range is no surprise.

    Here's one on Amazon:

    https://www.amazon.com/ProsKit-900-0...%2C5475&sr=8-4
    Last edited by Paul Alciatore; 04-05-2022, 12:33 AM.

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  • andywander
    replied
    #7-32 (with a nominal OD of 0.154") is listed as a standard screw size in my 1914 Machinery's handbook.

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  • The Metal Butcher
    replied
    Originally posted by sjaffe View Post
    Thanks for the replies. I have both SAE and metric thread gauges. 0.8 is 31.75 TPI. I compared 0.8 gauge and 32 TPI gauge with my fastener using a microscope. The 0.8 is just a slight bit off, the 32 TPI looks like a better match. I believe 0.8 translates to 31.75 TPI, hence why they would be close (but no cigar). I have not seen M4x0.8 listed (only 0.7 and 0.5). M4 major diameter specs show a minimum of 3.838 mm (0.151") so it could be an M4, but it seems unlikely that all the fasteners would be right at the minimum spec(?) So I'm not buying it's M4x0.8
    It is common for cheap threads to be undersized, hence why I suggested that. Measure a piece of 1/2" allthread, it's typically almost 20 thou under. I won't say it is for sure M4x.8, but that size exists on Google.

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  • Stepside
    replied
    If were mine and there is enough material to tap it #8-32 thats what I would do. Then I would order up some of the plastic caps that work with socket-head cap screws. They press into place with an Arbor Press, A Drillpress or a Vise.

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  • Georgineer
    replied
    Originally posted by BCRider View Post
    That would work but it would sure result in a sloppy fit. And the distinct risk of peeling the crests off the screws if you try to tighten something a little too much. Any chance of replacing the screws at the same time without too much extra work so the threads are all a proper #8?
    BC,
    As I understand Stan's original post, he's planning to make new 'upgraded' thumbscrews, so the issue of a sloppy fit wouldn't arise.

    Stan,
    Not oddball but historic!

    George

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  • BCRider
    replied
    That would work but it would sure result in a sloppy fit. And the distinct risk of peeling the crests off the screws if you try to tighten something a little too much. Any chance of replacing the screws at the same time without too much extra work so the threads are all a proper #8?

    I sometimes wonder about the missing in between sizes in some of the thread systems. For example Uncategorized Groups machine screws are out there. Not commonly but still available without too much fussing. So at one point in history were the other missing odd number sizes also out there? Like 1/8 and 3/16 screws used to be a size but they were replaced by number sizes at some point in the last century?

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  • MrWhoopee
    replied
    Originally posted by sjaffe View Post
    Thanks George. While I cannot confirm, this seems plausible and what I was suspecting (something oddball). I have no idea where this tool was made. It sounds like I might get away with just running an 8-32 tap through the existing tapped holes (8 size measured about 0.010" larger).

    Stan
    This is probably the best solution. 6-32 is a notoriously weak thread, M4x.8 would be even worse.

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  • sjaffe
    replied
    Thanks George. While I cannot confirm, this seems plausible and what I was suspecting (something oddball). I have no idea where this tool was made. It sounds like I might get away with just running an 8-32 tap through the existing tapped holes (8 size measured about 0.010" larger).

    Stan

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