ISO 2768 Title-Block Note Decoder

How to read the result

• Linear class is the first letter after ISO 2768: f fine, m medium, c coarse, v very coarse. It sets the ± deviation for every linear dimension that has no tolerance of its own.
• Geometric class is a second letter, H, K or L. It points to ISO 2768-2, so read the status line before you rely on it.
• Limits are the nominal size minus and plus the deviation, in millimetres and in inches.
• Share of nominal is the deviation divided by the nominal size, as a percentage. It shows how tight the class is at that size.
• Capital letters such as ISO 2768-MK are read as m plus K. The standard writes the linear class in lowercase and the geometric class in uppercase, and since f, m, c and v exist only as linear classes and H, K and L only as geometric classes, the letter itself is never in doubt. The result says when this happens.
• Anything after the class, such as -E in ISO 2768-mK-E, is shown as an unrecognised suffix. Check the drawing notes for what it asks for.
• A dimension that carries its own tolerance follows that tolerance, not the title-block note.

Where the values come from

The linear deviations and the external radius and chamfer values come from ISO 2768-1:1989. ISO last reviewed and confirmed that edition in 2022 and lists a revised ISO 2768 under development. For design release, check the values against the edition of ISO 2768-1 named on your drawing.

• Size bands run from 0.5 up to 3 mm, then over 3 up to 6 mm and on to over 2000 up to 4000 mm. Each upper bound belongs to its own band.
• The standard leaves two cells empty: class f over 2000 mm and class v from 0.5 up to 3 mm. The decoder returns no value for them.
• For nominal sizes below 0.5 mm, ISO 2768-1 says the deviation is written next to the dimension, so no general value is given.
• Inch figures are converted at 1 in = 25.4 mm and rounded to four decimals.
• ISO 2768-2:1989, the source of the H, K and L letters, was withdrawn on 2021-02-04 and revised as ISO 22081:2021. This page reproduces no geometric values.