“All references to percent of thread engagement have been eliminated from this document. Past changes in the thread form designation of the 'basic' thread height from 0.750H to 0.625H confused the calculation of percent of thread engagement. This calculation has been used in the past for threaded products users to determine drill size selection. It is now recommended that users select a drill size that will result in a hole size that lies between the maximum and minimum size of the internal thread's minor diameter shown in the tables included in this Standard.” (Unified Inch Screw Threads, ASME B1.1-2003, p. vi)

Projects for the Beginning Student Machinist - Connecticut State Dept Education