What is the Difference between bspt and bspp, and What is Represented by Rp and Rc?

BSP thread refers to the British standard pipe thread, which falls under the category of Whitworth thread (BS 84). BSP threads are divided into two types based on their shape (bspt and bspp): parallel pipe thread BSPP (British Standard Pipe Parallel) and tapered pipe thread BSPT (British Standard Pipe Taper). The thread angle for BSP threads is 55 degrees.

1. G = BSPP = BSPF = BSPM = PS

The letter “G” stands for “Gas” (some say it comes from the German word “Gewinde,” meaning “thread”), as it was initially used in gas pipelines. We refer to G as pipe thread because the first letter of “Guan” (pipe in Chinese) is the same as G.

G threads come in internal and external types and are used for non-sealing connections. The current standard is BS EN ISO 228-1, while the old standard BS 2779 is now obsolete.

Additionally, here are the meanings of some common versions of standards:

• ISO-xxx = International Standard
• EN-ISO-xxx = European version of the International Standard
• BS-EN-ISO-xxx = British version of the European version of the International Standard

2. R=BSPT=PT

BSPT – British Standard Pipe Taper, also known as PT thread, is used only for general sealing connections. The old standard for BSPT was BS 21, but in the new standard BS EN 10226-1, R threads have replaced it.

R threads are a series, commonly including Rp, Rs, Rc, R1, and R2. Specifically:

• Rp – British sealing parallel internal thread
• Rs – British sealing parallel external thread
• Rc – British sealing taper internal thread
• R1 – British sealing taper external thread, used with Rp, forming a”parallel/taper” fit (Rp/R1)
• R2 – British sealing taper external thread, used with Rc, forming a “taper/taper” fit (Rc/R2)

Thus, general sealing British pipe threads are divided into two types: parallel pipe threads and taper pipe threads.

The design of sealing parallel pipe threads (Rp) is identical to non-sealing pipe threads (G), except for the thread precision. Sealing taper pipe threads (R) are technically transformed from parallel pipe threads with a 1:16 taper. The design is as shown in the figure below:

3. BSP Thread≠ G Thread

It’s worth noting that many people think BSP threads refer to G threads and can be used interchangeably, but there are different opinions on this.

The sealing effect of general sealing parallel pipe threads (Rp) is achieved by adding sealing fillers (e.g., PTFE tape) throughout the thread, while the sealing effect of non-sealing parallel pipe threads (G) is achieved by using sealing devices (e.g., O-rings) at the ends or around the thread connection.

Moreover, the uses and design tolerances of general sealing pipe threads and non-sealing pipe threads are different. For details, refer to the《Metric, American, and British Thread Standards Handbook》.

Many machining companies often encounter issues where the thread ring gauge and plug gauge pass inspection, but the connection still leaks. This is mainly due to confusing sealing Rp internal threads with non-sealing G internal threads.

Some thread codes and standards related to BSP threads:

• G – British parallel pipe thread (standards: BS 2779, BS EN ISO 228-1, ISO 7-1)
• BSPP – British parallel pipe thread (standards: BS 2779, BS EN ISO 228-1, ISO 7-1)
• BSPT – British taper pipe thread (standards: BS 21, BS EN 10226-1, ISO 7-1)
• R (Rp, Rs, Rc, R1, R2) – British taper pipe thread (standards: BS 21, BS EN 10226-1, ISO 7-1, DIN 2999)

In conclusion, understanding the differences between bspt and bspp threads, particularly the distinctions between parallel (BSPP/G) and tapered (BSPT/R) threads, is crucial for ensuring proper sealing and functionality in pipe connections. While G threads are commonly used for non-sealing applications, Rp and R threads are designed for sealing purposes, with specific tolerances and design considerations. Misidentifying or misapplying these threads can lead to sealing failures, even if the threads pass standard gauge inspections. Therefore, it’s essential to refer to the appropriate standards, such as BS EN ISO 228-1 or BS EN 10226-1, and consult resources like the 《Metric, American, and British Thread Standards Handbook》 for accurate implementation. By paying attention to these details, manufacturers and engineers can avoid common pitfalls and ensure reliable, leak-free connections in their projects.

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