Short answer
A BSP thread identifies only the thread family of the connection; it does not on its own explain whether sealing is achieved with a flat seal, an O-ring, a cone seat or on the thread. For the correct fitting, the thread and seat geometry must be recorded separately.
Technical explanation
Parallel pipe threads within the scope of ISO 228-1 relate to applications where pressure tightness is not achieved on the threads themselves. Therefore, seeing a G thread does not determine which surface the connection seals on. Different BSP end designs may share the same nominal thread. The material of the sealing element, the mating surface and the tightening method must be taken from the actual connection design. The nominal inch size is not the angle of the cone surface or the seal size.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Thread family | BSPP/BSPT and its standard |
| Seat | Flat, cone or special surface |
| Seal | Type required by the design |
| Mating part | Port and connection surface |
How is it assessed in practice?
When sharing a sample with the supplier, do not send only a side photo of the thread; also show the end face and the port mouth. In the order description, specify the seat type after the phrase 'BSP thread'. If, on a spare part, you see a gap or different contact even though the thread engages, do not force the assembly. Adding an extra seal where the mating part has no surface designed for a seal should not be considered a solution. Ask for a dimensioned drawing to resolve the uncertainty. Do not assign tape, a seal or a tightening method to the connection before the thread family and the actual sealing surface have been determined together.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Does a BSPP connection always use a flat seal?
No. A BSPP thread can be used in different sealing designs; the actual connection geometry must be examined.
Source coverage
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S019
4 Easy Steps to Identify Hydraulic Threads Parker Hannifin · accessed 2026-10-19 PDF page 1-2: thread identification
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S069
ISO 228-1:2000 ISO · accessed 2026-10-19 Abstract; threads do not provide the pressure-tight joint