USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
CONVERSION CHART - FEET TO METERS.
(2) Unified System. Since the Whitworth and American National thread
forms do not assemble because of the difference in thread angle, the 60
thread angle was adapted in 1949.
However, the British may still use
rounded crests and roots and their products will assemble with those made in
United States plants. In the unified system, class signifies tolerance, or
tolerance and allowance. Fit is determined by the selected combination of
classes for mating external and internal threads. New classes of tolerance
are listed below: 3 for screws, 1A, 2A, and 3A; and 3 for nuts, 1B, 2B, and
(a) Classes 1A and 1B, Loose Fit.
A fit giving quick and easy
assembly, even when threads are bruised or dirty. Applications: Ordnance
and special uses.