BSP Fitting Size Chart: BSPP & BSPT Thread Dimensions

BSP fitting sizes can be confusing because the stated British Standard Pipe size does not match the measured outside diameter of the thread. BSP fittings may also use parallel or tapered threads, making it important to identify both the fitting size and BSP thread type.

Use this BSP fitting size chart to compare nominal British Standard Pipe sizes, approximate male-thread diameters and threads per inch. It can help identify BSPP and BSPT fittings, stainless steel adapters, valves, pumps, gauges and other fluid-handling components.

BSP Fitting Size Chart

Dimensions are approximate identification references. Male-thread measurements can vary slightly depending on thread taper, measurement location, manufacturing tolerance and thread condition.

What Does BSP Mean?

BSP stands for British Standard Pipe. BSP pipe threads are commonly found on imported pumps, valves, pressure gauges, regulators, filters, kettles, tanks and fluid-handling equipment.

BSP threads use a 55-degree Whitworth thread form. They are available as parallel BSPP threads and tapered BSPT threads.

What Is BSPP?

BSPP stands for British Standard Pipe Parallel. Both the male and female threads remain the same diameter along their length rather than becoming narrower or wider.

BSPP connections generally rely on a gasket, O-ring, bonded washer or another designed sealing surface. The straight threads primarily hold the components together and do not normally create the pressure-tight seal by themselves.

What Is BSPT?

BSPT stands for British Standard Pipe Taper. The thread diameter changes gradually along the threaded section, causing compatible male and female connections to tighten as they are assembled.

BSPT connections may require an appropriate thread sealant, depending on the fitting design, system requirements and manufacturer instructions.

How to Measure a Male BSP Fitting

1. Use a caliper to measure across the widest outside edges of the male threads.
2. Compare the measurement with the approximate thread diameter in the BSP chart.
3. Use a thread-pitch gauge to confirm the threads per inch.
4. Check whether the thread remains parallel or becomes tapered.
5. Confirm the fitting against a known BSP component whenever possible.

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How to Identify a Female BSP Fitting

Female BSP fittings are more difficult to identify using only an inside-diameter measurement. Measure the opening with a caliper, check the thread pitch and inspect whether the internal thread is parallel or tapered.

Whenever possible, compare the female port with a known BSP fitting or use a professional thread-identification gauge. Do not force an unknown male fitting into the connection.

Why Does the BSP Size Not Match the Measured Diameter?

BSP sizes are nominal pipe sizes rather than direct measurements of the thread diameter. For example, a 1/2-inch BSP male fitting has an approximate outside thread diameter of 0.825 inches—not 0.500 inches.

This difference is normal. Always compare the measured thread diameter and pitch with a BSP fitting chart instead of relying on the nominal size alone.

BSP Versus NPT Threads

BSP and NPT are different pipe-thread standards. They use different thread profiles and frequently use different thread pitches:

• BSP threads use a 55-degree thread form.
• NPT threads use a 60-degree thread form.
• 1/8-inch BSP uses 28 threads per inch, while 1/8-inch NPT uses 27.
• 1/4-inch BSP uses 19 threads per inch, while 1/4-inch NPT uses 18.
• 1-inch BSP uses 11 threads per inch, while 1-inch NPT uses 11.5.

Some BSP and NPT fittings may begin to thread together, particularly in sizes with similar diameters and pitches. This does not confirm compatibility and can result in damaged threads or an unreliable seal.

Can BSPP and BSPT Fittings Connect?

Certain systems are designed to use a tapered BSPT male thread with a compatible parallel female BSP thread. However, compatibility depends on the applicable standard, sealing method and fitting design.

Do not assume that any BSPP and BSPT components can be combined. Confirm the male and female thread design and follow the equipment manufacturer’s recommendations.

Common BSP Thread Markings

BSP fittings may use different markings depending on the standard and manufacturer:

• G commonly identifies a BSP parallel thread.
• R commonly identifies a tapered male BSP thread.
• Rc commonly identifies a tapered female BSP thread.
• Rp commonly identifies a parallel female thread intended for certain pressure-tight BSP connections.

Product names may also use labels such as male BSPP, female BSPP, male BSPT or female BSPT.

Choosing the Correct BSP Fitting

Before ordering a BSP adapter or replacement fitting, confirm:

• The nominal BSP size
• The approximate thread diameter
• The threads per inch
• Whether the thread is BSPP or BSPT
• Whether the connection is male or female
• The required sealing method
• The fitting material and pressure rating

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Browse stainless steel BSP fittings and adapters for pumps, valves, tanks, filters and other fluid-handling equipment. Available connections may include BSPP, BSPT, male, female and BSP-to-NPT adapters.

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If you are unsure which BSP fitting you require, compare the thread diameter and pitch with the chart above. Photographs, measurements and information about the connecting equipment can also help identify the correct BSP fitting or adapter.