BSP – British Standard Pipe

BSP threads have a 55° V-thread with rounded roots and crests. They are used throughout the world, except for the United States. This article discusses the features and dimensions of the BSP (British Standard Pipe) standard.

Table of contents

• What is the BSP thread standard?
• Labeling
• BSP vs NPT

What is the BSP thread standard?

The BSP, or Whitworth thread, is a family of thread standards that have been adopted internationally, except in the United States. This thread form has a 55° V-thread with rounded roots and crests, as seen in Figure 1. For a thread that conforms to BSP, the major diameter of the pipe thread is slightly smaller than the actual OD (outer diameter) of the pipe, and the minor diameter will be very close to (smaller than) the inside diameter of the female thread. There are two types of BSP threads:

• BSPP: Both the male and female threads are parallel. BSPP connections are widely used in the UK, Europe, Asia, Australia, New Zealand, and South Africa. Table 1 shows the dimensions of the BSPP standard.
• BSPT: The male threads are tapered, and the female threads are commonly parallel. BSPT connections are especially popular in China and Japan. Table 2 shows the dimensions of the BSPT standard.

Read our thread design article for more details on the various thread design parameters.

How to identify a BSP thread

First, find the thread’s inner diameter to determine the threads per inch count for the BSPT fittings. Use a vernier caliper to take a reading from inside the bore of the fitting. Then, cross check the bore size with thread pitch and threads per inch given in Tables 1-3 to find the desired size and its related specifications. Read our article on measuring threads for more details on how to use a vernier caliper to measure the thread diameter.

Click the button below to download the following charts.

Table 1: BSPP (G) – British Standard Pipe Parallel

Nominal Thread Size	Major Diameter (mm)	Minor Diameter (mm)	TPI (in-1)
G 1/16	7.723	6.561	28
G 1/8	9.728	8.566	28
G 1/4	13.157	11.445	19
G 3/8	16.662	14.950	19
G 1/2	20.955	18.631	14
G 3/4	26.441	24.117	14
G 1	33.249	30.291	11
G 2	59.614	56.656	11
G 3	87.884	84.962	11

Table 2: BSPT (R/Rp) – British Standard Pipe Tapered

Nominal Male Tapered Thread Size (inch)	Nominal Female Parallel Thread Size (inch)	Major Diameter (mm)	Minor Female Diameter (mm)	TPI (in-1)
R 1/16	RP 1/16	7.723	6.490	28
R 1/8	RP 1/8	9.728	8.495	28
R 1/4	Rp 1/4	13.157	11.341	19
R 3/8	Rp 3/8	16.662	14.846	19
R 1/2	Rp 1/2	20.955	18.489	14
R 3/4	Rp 3/4	26.441	23.975	14
R 1	Rp 1	33.249	30.111	11
R 2	Rp 2	59.614	56.476	11

Table 3: British Standard Pipe dimensions for standard thread sizes

Nominal G / R size (in)	Corresponding Pipe
	DN (mm)	Actual OD (mm)	Wall (mm)
1/16	3
1/8	6	10.2	2
1/4	8	13.5	2.3
3/8	10	17.2	2.3
1/2	15	21.3	2.6
3/4	20	26.9	2.6
1	25	33.7	3.2
2	50	60.3	3.6

Labeling

BSP threads are identified with letters, each of which represents the type of thread and their associated standards:

• G: external and internal parallel (ISO 228) - BSPP
• R: external taper (ISO 7, EN 10226, BS 21, DIN 2999, JIS B 0203) - BSPT
• Rp: Internal parallel (ISO 7-1, EN 10226) - BSPT
• Rc: internal taper (ISO 7) - BSPT
• Rs: external parallel (BS 21) - BSPT- Obsolete
  • ISO 7: Pipe threads where pressure-tight joints are made on the threads.
  • ISO 228: Pipe threads where pressure-tight joints are not made on the threads.

Example

• EN 10226 Rp 2 ½ : This refers to a British Standard Pipe thread tapered (EN 10226) with an internal parallel form (Rp) and a nominal size of 2 ½ inches.

BSP vs NPT

NPT/NPS threads have a 60° angle and have flattened valleys and peaks whereas BSP threads have a 55° angle and have rounded peaks and valleys. NPT/NPS and BSP threads are not compatible with each other due to the differences in their thread forms. Table 4 summarizes NPT and BSP standards’ threads per inch.

Table 4: NPT vs BSP threads per inch (TPI)

Thread size	Pitch (Threads per inch)
	NPT/NPS	BSP
1/8	27	28
1/4	18	19
3/8	18	19
1/2	14	14
3/4	14	14
1	11 1/2	11
1 1/4	11 1/2	11
1 1/2	11 1/2	11
2	11 1/2	11
2 1/2	8	11
3	8	11
3 1/2	8	11
4	8	11
5	8	11
6	8	11

Read our NPT, Unified thread standard, and M-Metric thread standards for more information on other thread standards.