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BELL SYSTEM TECHNICAL JOURNAL 



TABLE III 



tablished for reasons which were possibly good and sufficient but which 

 certainly have long been forgotten. Meanwhile, another subcommittee is 

 investigating the possibility of applying a similar series to the diameters of 

 wire. Probably diameters to 4 decimal places will be required. 



Dimensional Tolerances 



Part Tolerances 



Regardless of the dimension decided upon in a design it is obvious that it 

 cannot be regularly manufactured to the exact size. Certain manufac- 

 turing variations or tolerances must be expected and these introduce a large 

 share of our dimensional problems. 



The usual statement on tolerances is that the larger the tolerance 

 allowed the cheaper the part is to manufacture and, therefore, the tolerance 

 specified should be the widest that will permit functioning. However, 

 this is generally true only of overall tolerances which define the manufac- 

 turing methods that may be used. It is true in the sense that apparatus is 

 inexpensive to manufacture if it can be so designed that its functioning is 

 largely independent of variations in dimensions. However, such design is 

 not usually achieved and in much apparatus fairly good overall accuracy of 

 dimensions and fit is necessary for uniform functioning. The problem of 



