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Thread: Screw thread information and tables

  1. #21
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    Quote Originally Posted by juergenwt View Post
    Nice job Gordon. Since this is made up for shop use I think you should make reference to the fact that: For STANDARD metric thread the pitch is never given on a print. This is to let people know they are looking at the coarsest available thread for that size. These threads are used on over 90% of all metric parts. So it is not M16 x 2 but just M16. Every time you give a pitch like in M10 x 0.75 people will know they are looking at a metric fine thread. If you would see M10 x 1.5 on a print you would than be forced to look up a table to see what the standard is for M10. Most shops would only have the standard metric taps in stock. Most likely M2, M3, M4, M5, M6, M8, M10, M12, M16, M20 and may be M24. This would most likely cover 99% of all shops.This is important for US companies who are used to having a second number after the nominal size i.e. 1/4-20.
    I know ANSI allowed the use of listing the pitch on standard metric threads, but they messed up big time and now when American companies look at a metric print with no pitch listed for the thread- many have to inquire as to what the pitch is. In short: If no pitch is listed for a metric thread it is always the preferred STANDARD. Meaning the coarsest available thread for that size.
    Let me know what you think about this
    Screw thread types
    especially
    http://www.f-m-s.dk/1.07.pdf

    Is that what you had in mind? As far as I can see most American threads give the pitch automatically.

    Gordon

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    I found a mistake I made with the pitch of a thread. Hopefully I only made one mistake. this is the revised page:
    http://www.f-m-s.dk/Threads%20and%20pitches.pdf

    Contents is probably the most important page(s)
    http://www.f-m-s.dk/0.02Contents.pdf

  3. #23
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    A customer had a thread gauging problem so it gave me the incentive to add a new page. it's 4.04 THREAD INSPECTION USING THREAD PLUG & RING GAUGES

    Screw thread types

  4. #24
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    jhruska is offline Stainless
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    Gordon,
    Great Thread!

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    Quote Originally Posted by Gordon B. Clarke View Post
    I found a mistake I made with the pitch of a thread. Hopefully I only made one mistake. this is the revised page:
    http://www.f-m-s.dk/Threads%20and%20pitches.pdf

    Contents is probably the most important page(s)
    http://www.f-m-s.dk/0.02Contents.pdf
    I don't know why but I couldn't go in and edit that post. It would seem there was a broken link. Maybe this works?
    http://www.f-m-s.dk/Threads%20and%20pitches.pdf

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    juergenwt is offline Hot Rolled
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    Gordon - my tool and die makers had withdrawal symptoms when we changed to metric and I did not stock any fine metric screws, nuts, taps and dies.
    Explanation: Metric threads are designed so the coarse (standard) pitch is all you need for general shop use. Than it took some explaining to our engineers and to the designers to use standard and not give a pitch unless for a very special reason a fine thread is needed.
    I think in the last twenty years I ordered fine thread two ore three times.
    Engineer: Why can I not list the pitch - regardless if coarse or fine?
    Answer: If you start listing the pitch for coarse (standard) the tool maker will now have to check if this is a fine thread (special) or if this is the coarsest thread (standard) available for that size. Like I said, we used a fine thread on just a few occasions and for that special one time use a phone call to the nearest supplier was all that was needed.
    After a short time everybody got used to use only M2, M3, M4, M5, M6, M8, M10, M12 and M16.
    Big reduction of screws, nuts, taps and dies in our inventory and after a short time everybody got used to it When you looked at a die block and you saw what looked like an 8mm thread you knew it was a standard M8 not a fine thread.
    Advise to all shops: When putting in a supply of metric fasteners - use standard only. You will find out that is all that is needed. Keep any special taps, dies as well as nuts and bolts you may have ordered for a special job, under lock and key.

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    Quote Originally Posted by juergenwt View Post
    Gordon - my tool and die makers had withdrawal symptoms when we changed to metric and I did not stock any fine metric screws, nuts, taps and dies.
    Explanation: Metric threads are designed so the coarse (standard) pitch is all you need for general shop use. Than it took some explaining to our engineers and to the designers to use standard and not give a pitch unless for a very special reason a fine thread is needed.
    I think in the last twenty years I ordered fine thread two ore three times.
    Engineer: Why can I not list the pitch - regardless if coarse or fine?
    Answer: If you start listing the pitch for coarse (standard) the tool maker will now have to check if this is a fine thread (special) or if this is the coarsest thread (standard) available for that size. Like I said, we used a fine thread on just a few occasions and for that special one time use a phone call to the nearest supplier was all that was needed.
    After a short time everybody got used to use only M2, M3, M4, M5, M6, M8, M10, M12 and M16.
    Big reduction of screws, nuts, taps and dies in our inventory and after a short time everybody got used to it When you looked at a die block and you saw what looked like an 8mm thread you knew it was a standard M8 not a fine thread.
    Advise to all shops: When putting in a supply of metric fasteners - use standard only. You will find out that is all that is needed. Keep any special taps, dies as well as nuts and bolts you may have ordered for a special job, under lock and key.
    Juergen, IMO there's loads of logic and good old common sense in you reasoning and explanation

    Here where metric is normal, if the pitch is given with the diameter you can be pretty certain that it isn't a standard pitch for the thread. With American threads then letters are always included UNC, UNF, UNEF, UNS etc.

    In case anyone wonders why a fine pitch is sometimes used then it is the best way to keep something fastened that is subject to vibrations. A fine thread doesn't loosen as easilly as a course thread. Of coarse there can be other reasons but that is the main one

    BTW if your name is of Scandinavian origin then it was probably Jørgen Of coarse it could also be Germanic origin and spelled differently again.

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    Right on Gordon. There are many other reasons why someone would use a fine or extra fine thread. Fine adjustment comes to mind as well as not having enough material thickness or needing a shallow thread because of wall thickness or in some cases just wanting to be different. The main thing is that the standard will work just fine for all except for the real specials.That is when you add the pitch to the thread designation.
    Interesting post and btw Jürgen is German orig..

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    Quote Originally Posted by juergenwt View Post
    Since this is made up for shop use I think you should make reference to the fact that: For STANDARD metric thread the pitch is never given on a print. This is to let people know they are looking at the coarsest available thread for that size.
    Juergen

    Though I did grow up with metric, and do believe it is and should be easier for anyone to understand and use, I would like to point out a great flaw with the statement.
    A blueprint should not ever be open for interpretation!
    IOW a designation of M3 means and should mean absolutely nothing!
    Yes, I understand the the accepted convention is M3 = M3 x .5, but that requires knowledge and research. I strongly believe that anything on a print - let it be metric or imperial - should take all steps necessary to remove any and all possibility of misinterpretation and should be as clear and specific as possible.
    While you may prefer plain vanilla M3 callout on a print, I for one choose something like the one in front of me right now, which is .625-18-UNJF-3A.
    I don't know what the part is for and I don't care.
    I don't know what the engineer was thinking and I don't care.
    I don't know what other threads exist in the .625 diameter, and I don't care.
    What I care about is that the print calls for the above mentioned thread and nothing more nor less. Period!
    It has nothing to do with metric or imperial, rather it has everything to do with basic rules in blueprints and their purpose. No guesses, no assumptions, no approximations.
    What is stated is what it is, nothing more and nothing less.
    Last edited by The real Leigh; 11-20-2011 at 07:54 PM. Reason: typo

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    Quote Originally Posted by juergenwt View Post
    Right on Gordon. There are many other reasons why someone would use a fine or extra fine thread. Fine adjustment comes to mind as well as not having enough material thickness or needing a shallow thread because of wall thickness or in some cases just wanting to be different. The main thing is that the standard will work just fine for all except for the real specials.That is when you add the pitch to the thread designation.
    Interesting post and btw Jürgen is German orig..
    I hope this doesn't sound "snooty" but the reason I didn't mention the other uses for fine threads were that they were rather obvious. Still, what is obvious to one person isn't necessarily obvious to another

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    Quote Originally Posted by SeymourDumore View Post
    Juergen

    Tough I did grow up with metric, and do believe it is and should be easier for anyone to understand and use, I would like to point out a great flaw with the statement.
    A blueprint should not ever be open for interpretation!
    IOW a designation of M3 means and should mean absolutely nothing!
    Yes, I understand the the accepted convention is M3 = M3 x .5, but that requires knowledge and research. I strongly believe that anything on a print - let it be metric or imperial - should take all steps necessary to remove any and all possibility of misinterpretation and should be as clear and specific as possible.
    You may have grown up with the metric system but perhaps not when dealing with metric threads.

    Lets take the M3 you give as an example. It is NOT open to interpretation. If that is all that is given then everyone knows (who work with metric threads) that it in fact (for an external thread) it is M3x0.5-6g and M3x0.5-6H for an internal thread. If I saw all that written out for a metric thread my first thought would be, "Aha, it isn't standard" and I'd have to check.

    In the real (metric) world M3 gives as much information as the American thread you gave as an example.

    This link shows how easy it is to put all standard metric thread tolerances on one page for a specific tolerance. Look at the pages listed under 3.1 and 3.2.

    Screw thread types

    On this link I've written the thread and tolerance in full to explain what each part means.
    http://www.f-m-s.dk/1.03.pdf

    Asking for a M3 gives just as much information as asking for .625-18-UNJF-3A. BTW that tolerance (3A) for the UNJF thread isn't the "normal" standard - 2A is. If the onlly thing written was .625-18-UNJF then that would signify a 2A tolerance. The 3A is written to specify that it isn't a 2A that is required.
    With American threads 2A is to them as 6g is to metric external threads and 2B is to 6H for internal.
    This link gives a simple overview http://www.f-m-s.dk/ThreadTables.pdf

    If any of what I've written requires more explanation by anyone just ask and I'll try and answer. If you don't ask you never learn. I ask questions frequently LOL

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    There are those that think every time I write USA or American then I must be criticizing. This has never been the case. There are different ways of doing things and what is acknowledged as “normal” in one country is not necessarily the same in another.

    Personally I think the metric thread system is easier than the American but both systems have their advantages and disadvantages.

    For example the American tolerance system is basically easier than the metric in most cases.

    Pitch diameter tolerance class 2A is the foundation for all normal UN threads. UNC, UNF, UNEF etc.
    The 3 normal pitch diameter classes for external threads are 1A, 2A (standard) and 3A. For internal then 1B, 2B (standard) and 3B. 2A and 3A have a downward allowance from nominal pitch diameter to ensure there will always be clearance between the largest external thread and the smallest internal thread.

    If you know the pitch diameter tolerance for 2A then you basically know all other tolerances.
    If the tolerance class size for 2A (external thread) is 1 then:
    1A = 1.5x1, 3A = 0.75x1 and 1B = 1.95x1, 2B = 1.3x1 and 3B = 0.975x1.
    The allowance for class 2A and 1A from nominal is 0.3 x the 2A tolerance.

    This can be seen on for example
    http://www.f-m-s.dk/3.03.2.pdf

  13. #33
    SeymourDumore is offline Diamond
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    Quote Originally Posted by Gordon B. Clarke View Post

    Lets take the M3 you give as an example. It is NOT open to interpretation. If that is all that is given then everyone knows (who work with metric threads) that it in fact (for an external thread) it is M3x0.5-6g and M3x0.5-6H for an internal thread. If I saw all that written out for a metric thread my first thought would be, "Aha, it isn't standard" and I'd have to check.
    Silly discussion ....
    You say when you see M3, you know it's a standard thread BECAUSE you work with metric threads.
    As opposed to an end user, service personnel, parts department, etc etc. who might get in contact with the component and it's blueprint and is required to either repair, replace or otherwise do something with the part, such as perhaps re-tap it or get a mating bolt/nut.
    So when he or she looks in the catalog and sees 3 different designations beginning with M, or on the shelf sees M3 coarse or M3 fine, he/she is also to be fully versed in machining terminology and convention as to select the proper fastener.

    And also note, while many tap manufacturers designate standard metric taps as M3 ( or whatever the size might be ) there is an equal number of them that DO IN FACT write out the entire size, pitch and tolerance on the tap.
    The question now becomes that you guys with the full knowledge of metric thread designations get the message that this tap is somehow not standard, or that the manufacturer does not know the accepted convention, thereby their tap might be crap too?


    And no, it has nothing to do with US standards, nor with metric or imperial. If the US used a simple "THD-1/4" on a print, I'd still be bitchin'!

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    I don’t particularly like getting into this ”silly” discussion with you but you are way off track.

    Quote Originally Posted by SeymourDumore View Post
    Silly discussion ....
    You say when you see M3, you know it's a standard thread BECAUSE you work with metric threads.

    As do about 90% of the world population. Not all with threads but with the metric system.

    As opposed to an end user, service personnel, parts department, etc etc. who might get in contact with the component and it's blueprint and is required to either repair, replace or otherwise do something with the part, such as perhaps re-tap it or get a mating bolt/nut.
    So when he or she looks in the catalog and sees 3 different designations beginning with M, or on the shelf sees M3 coarse or M3 fine, he/she is also to be fully versed in machining terminology and convention as to select the proper fastener.

    No, and simply because there isn’t anything called M course. The M says that it is a course (standard) thread. As to M fine then that was true once upon a time but now several metric threads have more than one fine pitch and all are also called “fine”. When the metric thread doesn’t have a standard course pitch THEN the pitch MUST be given. When a tolerance for a M thread isn't given it is ALWAYS 6g for external and 6H for internal.

    And also note, while many tap manufacturers designate standard metric taps as M3 ( or whatever the size might be ) there is an equal number of them that DO IN FACT write out the entire size, pitch and tolerance on the tap.
    The question now becomes that you guys with the full knowledge of metric thread designations get the message that this tap is somehow not standard, or that the manufacturer does not know the accepted convention, thereby their tap might be crap too?

    I beg to differ. It’s guys that you that make what is in fact simple, very complicated. Do you wear a belt, braces and suspenders to hold up your pants?
    When tap manufacturers write the full designation on their taps this is usually because they have more than one tolerance class of tap in that particular diameter. Metric threads have several more tolerance classes than the American thread.


    And no, it has nothing to do with US standards, nor with metric or imperial. If the US used a simple "THD-1/4" on a print, I'd still be bitchin'!

    You’d be right to bitch here. THD – ¼” on a print says nothing as I can think of at least 10 ¼” threads it could be. The equivalent would be if I wrote M x 2mm (giving the pitch but not the diameter).
    Seymour, I can find it understandable that many American find the metric system hard to learn as you make it much more complicated than it is. Within metal engineering there are only 2 dimensions . mm and m. You'd be wanting to write cm, dm etc.

    In school in Scotland way back when (before the UK went "officially" metric) I was taught a bit about the metric system. Most of what I was taught was useless as when I came to countries that used the metric system I'd have been looked at with sheer surprise if I'd started spouting the nonsense I'd been taught.

    M8 and 5/16"UNC are almost identical. In 99% of all practical cases and uses that information says everything there is to know about the thread if it is external.

    M8 can be written as M8x1.25-6g and 5/16"UNC can be written as 5/16"UNC-18-2A. If that ISN'T what is wanted then, and only then, need it be written in full. I'm not to sure I'd like to order from someone that didn't know that. If I wasn't sure he did (or it was a life and death situation) then I'd write the thread out in full.

    Of course 18 TPI is 1.41mm so the pitches aren't identical
    5/16" is also 7.94mm

  15. #35
    juergenwt is offline Hot Rolled
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    I come from the "real" shop world on both sides. Metric and US customary system.
    It is safe to say that in a metric shop (outside the US) nobody even knows the pitch of a given M3, M4 etc.. So if a worker say's: I need a M12 x 30 screw he will get a M12 x 30mm long screw
    and nobody will ask M12 x 30 long by what pitch? M12 is what the print states and that is it. If he would say:" I need a M12 x 1.75 x 30 mm screw" than everybody would think that he is asking for a M12 fine thread screw. This would require a look into a book. Thread charts with listing of all inch sizes with the available pitches and tap drills, fractional drills, letter drills, number drills and the decimal equiv. as are common in all US shops, are totally absent in a metric shop.
    In a shop that uses the US customary system a worker will say: I need a 1/4 - 20 x 1" screw and that is what he will get. That is what the print state. If he would ask for a 1/4 x 1" long screw, the next question would be 1/4 - ?? x 1".
    In either system there is no confusion if the correct thread size is listed on the print. The advantage for the metric shop is: approx. 50% reduction of inventory on screws, nut, taps and dies and NO thread charts on the walls or little plastic cards in your shirt pocket.
    Last edited by The real Leigh; 11-20-2011 at 07:59 PM. Reason: typo
    Gordon B. Clarke likes this.

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    Quote Originally Posted by juergenwt View Post
    I come from the "real" shop world on both sides. Metric and US customary system.
    In a shop that uses the US customary system a worker will say: I need a 1/4 - 20 x 1" screw and that is what he will get.
    Just a small remark I doubt if anyone would say 1/4"-20. They'd more likely say 1/4"UNC. 1/4"UNF is 28TPI and 1/4"UNEF is 32TPI. If the tolerance isn't gven then it's 2A for external and 2B for internal.

    Of course not everyone has the library of thread standards that I have LOL
    I have one (of many) book with about 700 pages all on thread standards. I pluck from the standards what I believe to be relevant for the pages in my thread manual.

  17. #37
    SeymourDumore is offline Diamond
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    Quote Originally Posted by Gordon B. Clarke View Post
    Seymour, I can find it understandable that many American find the metric system hard to learn as you make it much more complicated than it is. Within metal engineering there are only 2 dimensions . mm and m. You'd be wanting to write cm, dm etc.

    For Christ's sake Gordon! Do you EVER try to understand someone's statement or just make something up about it and go with it?

    Just when and where did I say it is a metric thing that I have a beef with!
    What I've said - and you conveniently disregarded - is that a clear definition of a thread is more preferred simply because it leaves nothing for imagination or experience as it may be.
    Rest assured, I know just as much about metric as you do, and did so before I knew imperial even existed!

    Juergen

    I don't quite understand what you're saying.
    Both, the metric and the Imperial threads have customary coarse and fine threads. Other than the size, they serve exactly the same purpose.
    When coarse is needed, coarse is specified. WHen fine is called for, then fine it is.
    Sounds like in your shop you went with not only the metric threads, but with coarse-only metric threads.
    For inventory purposes, It would be absolutely no different in your shop if you've remained imperial but specified nothing but coarse threads. And then you too could say 1/4, #10, 1/2 bolt.
    And for the record, within certain fields in the US, it is also enough to specify nothing but the size, simply because everyone assumes the standard pitch for their field.
    AT the end of the day, what I am saying is that Metric threads alone DO NOT! reduce the required inventory in any way, shape or form.

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    Same nonsense tit-for-tat that we've seen before.

    Thread locked, and future such will be also.

    - TRL

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