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DimensioningDimensioning practices for metric drawings are similar to those for non-metric drawings, but there are some subtle differences. This material outlines the current practices.
Dimension Lines and Projection LinesProjection lines are used to indicate the extremities of a dimension. They are generally drawn up to 1 mm from the outline of the object.Dimension lines are used to label a particular dimension. They have one or more arrowheads, which are typically 3 mm long x 1 mm wide. Thin type B lines are used for both projection lines and dimension lines.
Linear DimensionsGenerally linear dimensions are in millimeters (millimetres).To avoid having to specify 'mm' after every dimension, a label such as 'all dimensions in mm' or 'unless otherwise stated all dimensions are in mm' is usually contained in the title block. If the dimension is less than one a leading zero should be used before the decimal point. eg. 0.5 After reduction to microfilm and subsequent re-enlargement, the decimal point may sometimes become unreadable. To avoid possible misreading of the dimension a comma is often used instead of a decimal point. eg. 0,5 25,7
Angular DimensionsAngular dimensions are usually specified in decimal degrees, degrees and minutes, or degrees minutes and seconds.eg. 27.5° 27°30' 27°30'16" If the angle is less than one degree a leading zero should be used. eg. 0.5° 0°30'
Dimensioning MethodsTwo methods of dimensioning are in common use.
Overall DimensionsWhen several dimensions make up an overall length, the overall dimension can be shown outside these component dimensions.When specifying an overall dimension, one or more non-critical component dimensions must be omitted.
Auxiliary DimensionsWhen all of the component dimensions must be specified, an overall length may still be specified as an auxiliary dimension.Auxiliary dimensions are never toleranced, and are shown in brackets.
Dimensions not to ScaleDimensions that are not to scale are underlined.
Dimensions not CompleteWhen a dimension line cannot be completely drawn to its normal termination point, the free end is terminated in a double arrowhead.
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