Published September 22, 2026 · MfgWorkbench editorial reference
Do not choose a pipe fitting by nominal size alone. NPT, BSPT and BSPP can look similar while using different thread geometry or sealing arrangements.
| Feature | NPT | BSPT / R family | BSPP / G |
|---|---|---|---|
| Thread form angle | 60° | 55° | 55° |
| External thread | Tapered | Tapered (R) | Parallel (G) |
| Nominal diameter taper | 1:16 | 1:16 for R | None |
| 1/4-size pitch | 18 TPI | 19 TPI | 19 TPI |
| 1/2-size pitch | 14 TPI | 14 TPI | 14 TPI |
| Sealing design | Specified threaded joint/sealant | Specified ISO 7 joint arrangement | Separate designed sealing feature |
The misleading half-inch example
A half-inch NPT and half-inch BSP fitting can both show 14 TPI. That agreement does not resolve the flank-angle and dimensional differences. A few turns of apparent engagement are not proof of a pressure-tight, mechanically sound connection.
Use diameter and pitch to narrow identification, then verify form, taper and the manufacturer’s connection code. Look for the sealing face or O-ring geometry. If one item is marked only “1/2,” request the complete specification.
Choose an adapter, not a forced joint
When two systems must connect, use a purpose-designed adapter with each end correctly specified. Its material, seal design and pressure/temperature rating must suit the service. Tape or compound cannot turn mismatched thread forms into a conforming connection.
Keep thread identification separate from fluid compatibility. A correctly threaded adapter can still be wrong for the fluid, corrosion environment or operating temperature. Follow the manufacturer’s installation method rather than using a universal torque found online.
A receiving-inspection checklist
Record nominal size, full thread designation, male or female form, seal type and part number. Check the certificate or drawing where required. Segregate visually similar fittings to avoid mixing them during assembly. The linked charts provide selected dimensions for initial identification, while calibrated thread gauges and the governing specification establish acceptance.
References and verification
Original explanations and worked examples by MfgWorkbench. Sources below support the stated concepts or selected reference data; they do not certify every example or a production application.
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