The largest opening establishes the basic size of a reducing
fitting. The largest opening is named first, except for bull head tees,
which are reducing on both runs and for double branch elbows where both
branches are reducing. The outlet is the largest opening and named last
in both cases.
In designating the openings of reducing fittings, they should be
read in the order indicated by the sequence of the letters a, b, c, and
d. In designating the outlets of side reducing fittings, the side
outlet is named last. In case of the cross, which is not shown, the
side outlet is designated by the letter e.
Table 3.1
