This part of BS 1916 gives guidance on tolerances, limits and fits
for engineering sizes up to 19.69 in. The recommendations apply
particularly to fits between cylindrical parts, designated as “holes”
and “shafts”, in which case the term “size” refers to the diameter of
the mating parts. The data may also be applied in appropriate cases,
by suitable selection of the grades of allowance and tolerances, to fits
between other than cylindrical mating parts, in which case the “size”
refers to a length, width or other dimension instead of to a diameter.
The system described in this British Standard comprises suitable
combinations of 16 grades of tolerance and 21 types of fit for both
hole and shaft, ranging from fits of extreme interference to those of
extreme clearance. All but very exceptional engineering requirements
are covered, from very coarse work to fine gauge manufacture.
A selection of fits for general use is given in Figure 4, and further
guidance on tolerances for shafts and holes for a wide range of fits
is given in Part 2 of this British Standard, but it is intended that a
particular industry or organization extracts and uses those limits which
suit its own product. A unilateral hole basis system is recommended
but a full range of holes suitable for use on a shaft basis system,
unilateral or bilateral, is also included in the tables.