What's the default tolerance for 'round' ISO dimensions?

Due to our legacy products and primary vendor preferences, I have been typically working in inches (sometimes with dual dimensions), using
the ANSI standard as primary. I am interested in gradually making the conversion to metric (especially for new products) and have been playing with the ISO dimensioning standard as my primary units. When using ANSI dimensioning, default tolerances are generally covered by notes in the title block (i.e. for all .xx two-place decimals the tolerance is +/-.010", .xxx three-place decimals are +/-.005", etc.). Can anyone tell me how this is handled with ISO dimensioning??
Example: By default, a diameter of 50.02mm would show up as '50.02' on an ISO drawing, assuming you had your default place value set to two- place decimals. However, a 50mm feature shows up on the drawing as '50' regardless of the place value you set. I understand this is the ISO standard, but then how do you know what the default allowable tolerance is for that feature? Surely, you wouldn't need to apply a specific tolerance to every dimension?
Any advice to a metric newbie would be appreciated!
-JOSH
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There is no default tolerance in ISO dimensions. The default tolerance practice in ANSI is wrong & outdated. For example .XXXX three-place decimals are +/-.005" when it applies for . 50" nominal diameter or 15.00" and that is wrong.
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What do you mean by "wrong"?
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I think what he means is in ISO standards the bigger the part the bigger the tolerance is allowed to be. It may be wrong for ISO standards but I feel that ISO standards are wrong too. Why should you allow for a bigger tolerance for a larger hole.Even going from a 3mm hole to a 3.1mm hole the tolerance gets bigger. Now that is wrong
Dale Dunn wrote:

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Josh, The standard is ISO 2768 (Untoleranced Dimensions) and it is in fact based on ranges of size and the sizes using three charts (Linear, Angular & Broken Edges/Chamfers & Radii)The types of dimensions are then further refined by designations; Fine, Medium, course & Very Course, which are based on manufacturing methods. We use "ISO 2768-m K". Example: A Linear value of 50 falls in the range of 30 to 120mm so ISO2768-m would interpret it as having a 0.3mm tolerance.
As a minimum, you'll also need DIN ISO 286 for Fit Tolerancing.
Good Luck
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Thank you ALL for your input! Does anyone recommend a good comprehensive reference book or website that covers these standards/ tolerances (aside from the standards themselves)?
As for ANSI being right or wrong, I've never had anyone argue with me over how to interpret a tolerance on an ANSI drawing, since everything you need to know is covered on the drawing itself, if not with dimension specific tolerances, then by the general title block tolerances. If you want to show a larger tolerance for a larger hole, then you can do so, but at least if you don't specify a tolerance, the drawing clearly covers it without the need for a reference book to be supplied to the machinist with each drawing.
-JOSH
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Josh,
Just as a side note about ISO tolerancing: it's not nearly as practical as it pretends itself to be. The ISO 2768 standard even invalidates itself by suggesting its tolerances should only be applied when functionality is impacted. (yes, it does say that) I find I don't even see many European sources using it correctly. I see actual fits tolerence callouts used more often. I'm sure I'll get flamed for this comment, but it's true from my experience. There's a recent interesting discussion about this at eng-tips: http://www.eng-tips.com/viewthread.cfm?qid=206463&page=1
Also, there is nothing wrong with the Inch decimal method in the ASME standard. It can be misused just as easily as any other system. It is more about discipline when detailing a design more so than the actual standard used.
Either way, I can only say do what is right for your own operation. :)
Matt
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828e4adb-e539-4943-af1d- Just as a side note about ISO tolerancing: it's not nearly as practical as it pretends itself to be. The ISO 2768 standard even invalidates itself by suggesting its tolerances should only be applied when functionality is impacted. (yes, it does say that) I find I don't even see many European sources using it correctly. I see actual fits tolerence callouts used more often. I'm sure I'll get flamed for this comment, but it's true from my experience.
I would not comment on what's right or wrong, but, as an European engineer, I do not recall of a drawing using ISO default tolerances. In fact I did not know that it even existed before this thread. Maybe I'm ignorant. The way I've always seen it (but again I may be short-sighted) and do every day, is put a general tolerance (ie +/-.1mm) and add more precise tolerance where needed.
But I surely should put my hands on this chapter and see what I can use.
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