BSP Thread Standards: ISO 228 (Parallel) and ISO 7 (Tapered)

BSP threads are governed by two ISO standards:

1. ISO 228 (BSPP): Defines parallel threads where the diameter remains constant. These require a sealing washer or BSP thread sealant to prevent leaks, as the threads themselves don’t form a seal. Common in low-pressure hydraulic systems and water pipelines.
2. ISO 7 (BSPT): Specifies tapered threads that narrow toward the end. The male thread compresses into the female fitting, creating a seal through deformation. Widely used in high-pressure gas and steam systems (BSP gas threads).

Both standards use a 55° thread angle, distinguishing them from NPT’s 60° angle. Proper adherence to these BSP thread standards ensures interoperability and safety across global industries.

---

BSP Thread Chart Breakdown:

Pitch, Diameter, and Thread Angle
A BSP thread chart provides key dimensions for identifying and matching fittings:

• Major Diameter: The largest thread diameter (measured in inches or millimeters).
• Pitch: Distance between thread peaks (e.g., BSP thread pitch of 14 threads per inch for G1/2).
• Thread Angle: Always 55° for BSP.

Sample BSP Pipe Thread Chart Table

Thread Size	Major Diameter (mm)	Pitch (TPI)	Type
G1/8	9.73	28	Parallel
R1/2	20.99	14	Tapered

To read a chart, match measurements using a BSP thread gauge or caliper. For example, a fitting labeled “R3/4” refers to a tapered thread with a 26.44 mm major diameter.

---

Applications in Industrial and Plumbing Systems

• Hydraulics: BSPP threads are used in machinery due to their ability to withstand high pressures with proper sealing.
• Pneumatics: Air compressors often use BSPT for airtight connections in gas lines.
• Plumbing: BSPP dominates water supply systems, paired with sealant or washers.
• Oil/Gas: BSPT’s tapered design prevents leaks in volatile environments.

---

BSP vs Other Threads: NPT, Metric, and UNC

• NPT: Uses a 60° angle and tapered design. BSP vs NPT threads are incompatible without adapters due to differing pitches and angles.
• Metric: Measured in millimeters, but some BSP fitting sizes overlap (e.g., G1/2 ≈ 20 mm).
• UNC: Coarser pitch; rare in fluid systems.

Thread Compatibility Quick Reference

Thread Type	Angle	Seal Type	Common Use
BSPP	55°	Washer/Sealant	Low-pressure water
BSPT	55°	Thread Deformation	Gas/Steam
NPT	60°	Tapered	U.S. pipelines

---

Tips for BSP Thread Identification

1. Use a BSP thread gauge to measure pitch.
2. Calipers determine major diameter.
3. Check for taper visually or with a fit test.

---

.

.

FAQ

Conclusion

Mastering BSP thread charts is essential for engineers and technicians. Professionals can ensure durable, leak-free systems across industries by adhering to ISO 228/7 standards, using precise measurement tools, and understanding BSP thread compatibility. Always prioritize accurate BSP thread identification and consult the pipe Schedule Chart alongside other reference materials for optimal results.