The difference between BSPP and BSPT connections

Technical explanation

ISO 228-1 covers threads for connections where pressure-tight joints are not made on the threads; ISO 7-1 covers the corresponding pipe threads for pressure-tight joints. The G designation and the R, Rp or Rc designations must not be written interchangeably. In a parallel-threaded connection, sealing may be provided by a design such as a face, a seal or a cone seat. The nominal inch value alone is not the actual thread diameter or the sealing geometry.

Source: S019, S069

Topic-specific checkpoints

Source: S019, S069

How is it assessed in practice?

Clean the sample and exclude the damaged first thread from measurement. On an accessible male thread, measure the diameter at the area where the full thread begins and at an area farther away, holding the caliper jaws perpendicular to the axis; a change suggests taper. Determine the pitch with a suitable thread gauge and compare it with the nominal size table. Then record the port mouth, seal location and cone seat separately. If a reliable measurement cannot be taken on a female thread, ask for a mating part or manufacturer drawing. Do not consider parts that engage for a few turns as compatible, and take the tightening method from the relevant manufacturer's instructions.

Original editorial recommendation; not a clause of a standard.

Frequently asked questions

Are G 1/2 and R 1/2 the same connection?

No. Their designations are different; they must not be used interchangeably without checking their geometry and sealing method.

Source: S019, S069