G Series - Formally known as BSPF
The BSPP Thread Gages conform to to BS EN ISO 228-1 Parts and -2 for Gages. The standard year is 2003.
Screw Thread Ring Gages are available in Class A and Class B
Class A on G Series rings is more common and considered standard. Class B only refers to rings, there is no class B on screw plugs
The go thread ring gauge is a class A only.Class B does not exist but you may get inquiries asking for a Class B go ring in which case we will mark the Class A as a class B.
The difference is only on the No go ring. Class A is a tighter tolerance than a Class B, The tolerance on a class B is twice that of the Class A.
In March 2003 the British Standards Institute withdrew BS-2799 and replaced it with ISO-228 ( technically BS-EN-ISO-228 )
Full Form British Thread Gages sold by Thread Check Inc are full form gages traceable to U.K.A.S