This International Standard specifies tolerances on wrench and socket openings for screws and nuts (or similar Parts) having metric width across flats dimensions, as shown diagrammatically below.
It gives, for each dimension, the tolerances for general use, defined by its two deviations, minimum and maximum, with respect to the nominal value.
These deviations have been determined in relation to the width across flats tolerances for screws and nuts specified The nominal dimensions given in table 1, in addition to the standard values of the metric widths across flats specified in ISO 272, show a certain number of possible intermediate values indicated in parentheses.
ISO 691:1997 history
2005ISO 691:2005 Assembly tools for screws and nuts - Wrench and socket openings - Tolerances for general use
1997ISO 691:1997 Assembly tools for screws and nuts - Wrench and socket openings - Tolerances for general use
1983ISO 691:1983 Wrench and socket openings; Metric series; Tolerances for general use
1975ISO 691:1975 Title missing - Legacy paper document