This Standard specifies the thread form, series, class, allowance,
tolerance, and designation for
unified screw threads. (In order to emphasize that unified screw
threads are based on inch modules,
they may be denoted unified inch screw threads.) Several variations in
thread form have been
developed for unified threads; however, this Standard covers only UN
and UNR thread forms.
For easy reference, a metric translation of this Standard has been
incorporated as Nonmandatory
Appendix C. Nonmandatory Appendices A through E contain useful
information that is supplementary to
the sections of this Standard.