Applicable Standards
UNIFIED thread gauges (No.4 - 8")
Gauging practice: conform ANSI/ASME B1.2 - 1983 Diameter - TPI combination:
Thread plugs under 2.1/2" nominal diameter(inclusive) are manufactured double-ended (Go-NoGo) and above single-ended (Go or NoGo).
Tolerance class
Tolerance class for plug gauges (internal threads)
Tolerance class for ring gauges (external threads)
Application
1B
1A
where quick assembly is needed even when threads are dirty / damaged, wide tolerances for male and female threads
2B
2A
corresponds to medium fit and used for general applications which requires free assembly
3B
3A
where closer fit is required
AG class thread ring gauges are used in lubricant and high temperature applications.