BSPP Threads: Class A Grade Vs. Calss B Grade

What Are BSP Threads?

BSP (British Standard Pipe) threads are commonly used in Australia and Commonwealth countries. They are defined by trade size, not actual diameter, which can cause confusion when measuring ports. There are two types of BSP threads(BSPP threads and BSPT threads):

• BSPP (G): Both male and female threads are parallel, and meets ISO 228-1 standard.
• BSPT (R/Rp): The male thread is tapered, and the female thread is usually parallel (BSPP) but can also be tapered (Rc, though this is rare). BSPT thread meets ISO 7-1 standard.

Both BSPP and BSPT share the same pitch, a 55-degree angle, and rounded peaks and valleys. Despite the naming, it’s common to refer to the combination of a parallel female and tapered male as BSPT.

Calss Grades of  BSPP Threads

The class-of-fit designation applies specifically to BSPP female threads and the corresponding ring gauges. Under the ISO-228 specification, two classes of fit are defined for BSPP male threads: Class A and Class B.

Similarities and Dissimilarities of Class A and Class B(BSPP Threads)

Both Class A and Class B in the ISO-228 G threads have the same basic size, so the GO gauge can be used for both classes and may be marked as A, B, A/B, or unmarked.

Class A has tighter tolerances, making it the Precision Class, with higher production costs but savings on gauges since the Class A NOGO gauge can verify both classes. Class B has looser tolerances, reducing production costs, but its NOGO gauge is less common, more expensive, and has longer lead times.

Conclusion:

For G thread ring gauges, buy a GO gauge for both classes. For Class A, get the Class A NOGO gauge. For limited Class B production, a Class A NOGO gauge works, but for larger runs, use a Class B NOGO gauge. Consider both NOGO gauges for varying production needs.

QC Hydraulics is a leading manufacturer of stainless steel hydraulic fittings, BSPP, BSPT, NPT, NPTF, JIC, ORFS… all threads are available. Please contact us for more details.