Dimensioned in Fractions

The dual dimensioned drawing must identify which units are U.S. customary and which units are SI. Two methods are available for distinguishing groups: the position method and the bracket method.

In the position method of dual dimensioning, the millimeter-dimension is above the inch-dimension and separated from it by a horizontal line, or the millimeter-dimension is to the left of the inch-dimension and
separated from it by a slash. The following examples illustrate these methods:

One method of identifying inch- and millimeter-positions should be used consistently on a single drawing. The drawing must contain an illustration or note giving the positions of the inch- and millimeter-dimensions.Typical examples for this purpose are:

The bracket method is to enclose either the millimeter-dimension or the inch-dimension in square brackets, i.e., [ ]. This must be done consistently for a single drawing. The position of the bracketed dimension can be above, below, to the right of, or to the left of the other aspect, the place to be consistent to the extent practical in a single drawing. Examples are:

Existing illustrations which are dimensioned in fractions of an inch can be dual dimensioned simply by adding the millimeter-equivalents adjacent to the inch-dimensions. It generally is assumed that the accuracy
implied is equivalent to that of a decimal with two significant digits to the right of the decimal. Typical examples are:

Usually, it is desirable to express all fractions in a drawing as decimal fractions except where the portion designates nominal sizes. Nominal sizes are not converted or dual dimensioned.

This includes nominal thread sizes, pipe sizes, wood cross-sectional sizes, etc. Units for quantities other than length, which appear on dual dimensioned drawings, can and should be expressed as double dimensions and in the same manner as the dimensions of length.

This is true for units in notes and text, as well as units that appear on the part drawing. In general, any of the methods for dual dimensioning lengths given in the preceding paragraphs can be used. Values of density in U.S. customary units and SI units, as examples, can be specified in a drawing in the following ways on this website.

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