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➢ A minimum spacing between the object and dimensions and between dimensions

must be maintained.

➢ A visible gap shall be placed between the end of extension lines and the feature

to which they refer.
➢ Manufacturing methods should not be specified as part of the dimension unless

no other method of manufacturing is acceptable.

➢ Placing dimensions within the boundaries of a view should be avoided whenever
practicable.

➢ Dimensions for materials typically manufactured to gages or code numbers shall

be specified by numerical values.

o
➢ Unless otherwise specified, angles shown on drawings are assumed to be 90
➢ Dimensioning to hidden lines should be avoided whenever possible. Hidden lines
are less clear than visible lines

➢ The depth of blind, counterbored, or countersunk holes may be specified in note

along with the diameter.
➢ Diameters, radii, squares, counterbores, spot faces, countersinks and depth

should be specified with the appropriate symbol preceding the numerical value.

➢ Leader lines for diameters and radii should be radial lines.

4.9 Tolerances

Tolerance is the total amount a dimension may vary and is the difference between the

upper (maximum) and lower (minimum) limits. It is used to control the amount of
variation inherent in all manufactured parts. In particular, tolerances are assigned to

mating parts in an assembly.

One of the great advantages of using tolerances is that it allows for interchangeable parts,

thus permitting the replacement of individual parts. Tolerances are used in production
drawings to control the manufacturing process more accurately and control the variation

between parts.