USED FOR:
Pipe threads where pressure-tight joints are made on the threads
Tapered (BSPT) and parallel (BSPP) pipe thread dimensions and tolerances for threaded joints intended to be pressure-tight without additional sealing elements.
RELATED STANDARDS:
- ASME B1.20.1 “Pipe Threads, General Purpose (NPT), Inch”
- ISO 228-1 “Pipe threads where pressure-tight joints are not made on the threads – Part 1: Dimensions, tolerances and designation”
- EN 10226-1 “Pipe threads where pressure tight joints are made on the threads – Part 1: Taper external threads and parallel internal threads – Dimensions, tolerances and designation”
- ISO 7-2 “Pipe threads where pressure-tight joints are made on the threads – Part 2: Verification by means of limit gauges”
DIMENSIONAL RANGE:
This is dimensional in the classic sense, though expressed as thread size rather than pipe OD or DN: ISO 7-1 covers sizes from 1/16 up to 6 inclusive, using the same inch-based size designation (R, Rp, Rc) as ISO 228-1 rather than DN or NPS. The thread form itself follows a 55° Whitworth angle with a 1:16 taper ratio for the tapered (R/Rc) series, while the parallel (Rp) internal thread shares its actual diameters and pitches with ISO 228-1, which is exactly why the two standards get confused despite defining functionally different joints. We treat the size range and the R/Rp/Rc designation, not a DN or NPS figure, as the real identifying dimension when checking a threaded connection against this standard.
DESCRIPTION:
Relevant mainly for small-bore instrument connections, utility piping, and, notably , the threaded seacock and through-hull fitting connections referenced directly by the marine small-craft standards below. It’s a document we keep close whenever a project mixes NPT (American) and BSP (ISO/European) threaded fittings, since the two are not interchangeable despite superficially similar appearance.
IMPORTANT NOTES:
Mixing NPT and BSP fittings on the same connection is a classic and dangerous error, the thread forms are geometrically incompatible even where nominal sizes appear to match.