Figure 4.11 A table showing examples of nominal and actual sizes for framing lumber and boards.
In design engineering, size is used for purposes of general identification; the actual size of a part will be approximately the same as the nominal size but need not necessarily be exactly the same. For example, a rod may be referred to as 1/4 inch, although the actual dimension on the drawing is 0.2495 inch; in this case 1/4 inch is the nominal size.
The phrase "geometric dimensioning and tolerancing" (GDT) refers to the allowable variation of a dimension. It represents the difference between the maximum and minimum acceptable limits. All dimensions except basic, reference, nominal, maximum, or minimum dimensions must have a tolerance. GDT is a method of specifying the functional geometry of an object.
Understanding the international engineering language of GDT is essential for communicating in today's highly competitive global marketplace. You are required to read and interpret GDT symbols, which provide detailed information about the function and relationship of the various part features.
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