Manual of Engineering Drawing, 3rd Edition

Chapter Limits and fits

To ensure that an assembly will function correctly, its component parts must fit together in a predictable manner. Now, in practice, no component can be manufactured to an exact size, and one of the problems facing the designer is to decide the upper and lower limits of size which are acceptable for each of the dimensions used to define shape and form and which will ensure satisfactory operation in service. For example, a dimension of 10 ± 0.02 means that a part will be acceptable if manufactured anywhere between the limits of size of 9.98 and 10.02 mm. The present system of manufacture of interchangeable parts was brought about by the advent of and the needs of mass production, and has the following advantages.It should ...