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Thread: ISO hole size tolerance

  1. #1
    Associate Engineer
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    Mar 2020
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    ISO hole size tolerance

    Hello,
    I am accustomed to working with inch tolerances. More of my customers are requiring documents in the metric system.
    I have been studying the ISO tolerance charts and I don't get it.
    In the inch system you had (2) basic fits close and free fit (Machinery Handbook).

    In ISO the closest thing to a free fit is H14.
    An 8mm-H14 clearance hole is +0.36mm (0.014 in). That is not a free fit.

    Is there a standard for decimal place equivalent mm tolerance?
    0.0=+/- 0.5mm
    0.00=+/-0.25mm

    Thank you,

  2. #2
    Administrator Kelly Bramble's Avatar
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    Feb 2011
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    Bold Springs, GA
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    By industry standard, both ISO ad ASME (ANSI), inch units are expressed with trailing zeros of same significant figures but not leading zeros.

    And, ISO and ASME specifies that SI units, or mm are to be expressed with leading zeros but not trailing zeros nor is significant number of figures to maintained.

    Therefore, one cannot use the matching significant figure method to express default tolerances when using SI units.

    You may need to study up on ASME, ANSI and ISO dimensioning and tolerancing standards.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
    Join Date
    Mar 2020
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    2
    Thank you,

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