The math done by AMFAS assumes that the .085 undercut and NPT thread must meet at the same
exact longitudinal point.
This is not the case.
The 9/16” MAX. THREAD dimension specifies that the thread cannot exceed
.5625”, it is acceptable that the thread length is less than .5625”, but
must be at least .546” per the ANSI B1.20.1 requirement (effective thread).
This specification was added to ensure that the thread does not cut into the chamfer that extends to the left
(when viewing the SECTION A-A) from the .085” undercut.