Abstract
This paper discusses the new British Standard for limits and fits for Engineering (B.S. 1916), outlining in particular the technical features and explaining how the system has been built up. A brief historical review of other systems is made, their faults being referred to. The prospects of adoption of an equivalent system by the United States and a corresponding decision already taken by Canada are mentioned.
The paper goes on to discuss the theoretical requirements of a good tolerance system and then compares the new standard with the theoretical desiderata. The technical reason for each particular diameter step, tolerance value, or shaft or hole allowance is given, supplementing the necessarily bare data given in the standard itself.
Indications are given of the future extensions of the system which are likely to be made following international discussions in relation to tolerances for small diameters as used in the horological industry, tolerances for precision fits and fine quality gauges, and tolerances for large diameters up to about 6 feet. The practical difficulties in determining and using tolerances in diameters above 20 inches are considered in some detail, and a plea is made for discussion and information on this matter.
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