Dimensions are used not only to limit the size of a piece but also to enable a purchaser and user to check what is received.
Figure 1 illustrates how to dimension for both production and inspections. What is wanted is shown along with how it will be inspected. Doing this assures pieces which meet the requirements shown on the print.
Always dimension from a common datum line or surface and include concentricity symbols where applicable.
Figure 2 also illustrates how dimensioning for measuring is important. Since a portion of the outside surface is removed to produce the keyway or axial groove, dimension D is not equal to dimension A. By using dimension C, the depth of the groove B can be measured from a known surface. Only dimensions A and C are required to show the groove depth.