Everything you wanted to know about taps but were afraid to ask, styles of taps, class of thread , gh numbers , basic point in thread measurement , constants for finding pitch
The Difference Between 2A & 3A Threads Part 2 - Wilson-Garner
Unified Thread Standard - Wikipedia
Product and Technical Support Resources | Vermont Gage
Thread Chart (UNF-UNC) | Major and Minor Diameters
Screws
KATOpedia | Ground Thread Tap Limits for KATO STI Taps
Unified Thread Standard
Class of Threads, H Limits - Tapmatic Corporation
Understanding Class of Fit Tap Tolerance for UNC/UNCF - NEXT GENERATION TOOLING