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Expert Guide to What are BSP thread sizes: Identify BSPP vs BSPT in 3 Practical Steps

Dec 8, 2025 | Industry News

Abstract

An examination of British Standard Pipe (BSP) threads reveals a system of screw thread standards widely adopted for interconnecting and sealing pipes and fittings. This article provides a comprehensive analysis of what are BSP thread sizes, addressing the fundamental distinction between the two primary types: parallel threads (BSPP) and taper threads (BSPT). It traces the historical origins of the standard to Joseph Whitworth’s innovations and contextualizes its codification under international standards such as ISO 7 and ISO 228. The discourse methodically details the geometric properties, sealing mechanisms, and designation conventions for both BSPP (G-series) and BSPT (R-series) threads. Furthermore, it presents a practical methodology for accurate thread identification, involving visual inspection, precise measurement with calipers and gauges, and cross-referencing with standardized charts. The analysis extends to a comparative study against the American National Pipe Thread (NPT) standard, highlighting critical differences in thread angle and profile that preclude interchangeability. The functional role of BSP threads across diverse sectors, including fire protection, plumbing, and pneumatics, is explored, underscoring the importance of correct specification for system integrity and safety.

Key Takeaways

  • BSP threads come in two main types: parallel (BSPP or G) and tapered (BSPT or R).
  • Sealing for BSPP is at the face with a gasket; BSPT seals on the threads themselves.
  • The nominal size of a BSP thread refers to the pipe’s bore, not the thread’s diameter.
  • Understanding what are BSP thread sizes is vital for international equipment compatibility.
  • Never interchange BSP and NPT threads due to different angles and pitches.
  • Correctly identify threads using visual checks, calipers, and pitch gauges.
  • Always use thread sealant with BSPT connections to ensure a leak-proof joint.

Table of Contents

A Foundational Inquiry: What are BSP Thread Sizes?

To begin an investigation into the world of piping and fluid dynamics, one must first grapple with the connectors that hold these systems together. The question, “What are BSP thread sizes?” opens a door to a system of standardization born from industrial necessity, a system that affects engineers, technicians, and mechanics across the globe, particularly in regions that adhere to European and Commonwealth engineering traditions. Understanding this standard is not merely an academic exercise; it is a practical imperative for ensuring safety, efficiency, and compatibility in countless applications, from firefighting apparatus to domestic plumbing.

A Historical Perspective: The Whitworth Legacy

Before we can appreciate the structure of BSP, we must look to its origins. Imagine the state of manufacturing in the early 19th century. The Industrial Revolution was in full swing, but a peculiar kind of chaos reigned. Every workshop, every factory, had its own system for nuts, bolts, and screws. A bolt made in Manchester would not fit a nut made in Birmingham. This lack of uniformity was a tremendous source of inefficiency and frustration.

The person who brought order to this chaos was Sir Joseph Whitworth. In 1841, he proposed a standardized system for screw threads. His system was elegant and based on two key principles: a fixed thread angle of 55 degrees and a standard thread pitch (the number of threads per inch) for each diameter. A defining feature of the Whitworth thread form is its rounded crests and roots. This rounded profile, unlike the sharper angles of other designs, distributes stress more effectively, making the thread more resistant to stripping and fatigue. This innovation was revolutionary, and the British Standard Whitworth (BSW) system became the world’s first national screw thread standard. The British Standard Pipe (BSP) thread is a direct descendant of this foundational work, applying Whitworth’s 55-degree angle and rounded profile to the specific needs of pipes.

Defining the British Standard Pipe (BSP)

The British Standard Pipe is a family of technical standards for screw threads that has been adopted internationally. It governs the geometry of threads used to connect and seal pipes and fittings. While it originated in Great Britain, its utility has led to its formalization under the International Organization for Standardization (ISO). Specifically, BSP threads are technically defined by two main standards:

  1. ISO 228: This standard defines “Pipe threads where pressure-tight joints are not made on the threads.” These are the parallel threads, commonly known as BSPP.
  2. ISO 7: This standard defines “Pipe threads where pressure-tight joints are made on the threads.” These are the tapered threads, known as BSPT.

Grasping this distinction between threads that seal and threads that simply fasten is the first step toward mastering the BSP system. One type provides a mechanical connection, relying on a separate component for the seal, while the other creates the seal through its own geometry.

The Core Concept of Nominal Size

Here we encounter the most common point of confusion for newcomers. When we speak of a “1-inch BSP thread,” our intuition, shaped by everyday measurement, tells us that something about this thread should measure one inch. This is not the case. If you take a pair of calipers and measure the outside diameter of a 1-inch male BSP thread, you will find it measures approximately 1.309 inches (33.25 mm).

This discrepancy arises because the nominal size of a BSP thread does not refer to the physical diameter of the thread itself. Instead, it refers to the nominal bore, or internal diameter, of the steel pipe for which the thread is intended. Decades ago, pipe manufacturing technology was such that a pipe with a 1-inch internal bore had a specific, much larger, outer wall thickness. The threads were cut onto the outside of this pipe. So, the “1-inch” designation became a trade name, a label that referred to the pipe’s flow capacity rather than its physical dimensions.

Think of it like buying lumber. A “2×4″ piece of wood is not actually 2 inches by 4 inches; its finished dimensions are closer to 1.5 by 3.5 inches. The name is a historical remnant, a nominal size that everyone in the trade understands. The same logic applies to what are BSP thread sizes. The designation (e.g., 1/4″, 1/2″, 1”) is a name, not a direct measurement. The actual physical measurements are what we use for identification, which we will explore in detail.

The Principal Division: BSPP (G-Series) vs. BSPT (R-Series)

The BSP family is split into two distinct branches, each with a different geometry and sealing method. Mistaking one for the other is a common error that can lead to leaks, damaged components, and system failure. A clear understanding of their differences is therefore of paramount importance.

Understanding BSPP – The Parallel Path

BSPP stands for British Standard Pipe Parallel. As the name suggests, the threads on a BSPP fitting run parallel to one another along the entire length of the fitting. Imagine a simple cylinder with threads cut into it; the diameter at the beginning of the thread is the same as the diameter at the end.

Because the threads are parallel, they cannot form a seal by themselves. When a male BSPP fitting is screwed into a female BSPP port, there is no interference or wedging action. The threads serve a purely mechanical function: they clamp the two components together.

So, how does a BSPP connection seal? The seal is achieved by compressing a soft material between a shoulder on the male fitting and the face of the female port. This is typically accomplished with a bonded seal (also known as a Dowty washer), which is a metal washer with a vulcanized rubber ring on its inner diameter. Alternatively, O-rings, gaskets, or sometimes a machined metal-to-metal face seal can be used. The threads provide the force to compress this sealing element, creating a highly reliable, pressure-tight joint.

BSPP threads are formally designated with the letter G, according to the ISO 228-1 standard. For instance, a one-quarter-inch parallel pipe thread is denoted as G 1/4. The ‘G’ is a legacy from the German term Gasgewinde (gas thread), as these threads were historically common in gas lines.

Understanding BSPT – The Tapered Solution

BSPT stands for British Standard Pipe Taper. In contrast to BSPP, the threads on a BSPT fitting are cut on a cone. The diameter of the thread changes along its length. For an external (male) thread, the diameter gradually decreases from the start of the thread to the end. For an internal (female) thread, the diameter gradually increases.

This taper is the key to its sealing mechanism. When a male BSPT fitting is screwed into a female BSPT port, the threads interfere. The flanks of the male and female threads are forced together, creating a seal through a process of deformation and wedging known as thread interference. This is a metal-to-metal seal.

However, due to imperfections in manufacturing, this metal-to-metal seal is rarely perfect. Small helical leak paths can exist along the crests and roots of the threads. To fill these voids and ensure a fully pressure-tight seal, a thread sealant is almost always required. This can be a liquid or paste-like pipe dope or, more commonly, PTFE (Teflon) tape. The sealant fills any microscopic gaps, lubricates the threads to prevent galling (a form of wear caused by adhesion between sliding surfaces), and allows the fitting to be tightened to the correct torque.

BSPT threads are governed by ISO 7-1 and have several designations:

  • R: This denotes an external (male) tapered thread. For example, R 1/2.
  • Rc: This denotes an internal tapered thread. For example, Rc 1/2.
  • Rp: This denotes an internal parallel thread, designed to mate with an R-series external tapered thread. For example, Rp 1/2.

The most common combination is a male R thread sealing with a female Rc or Rp thread.

A Comparative Analysis: BSPP vs. BSPT at a Glance

To consolidate our understanding, a direct comparison is useful. The table below outlines the defining characteristics of each thread type, providing a clear reference for distinguishing between them.

Feature BSPP (British Standard Pipe Parallel) BSPT (British Standard Pipe Taper)
Geometry Parallel threads, constant diameter. Tapered threads, diameter changes along the length (1:16 taper).
Sealing Method Mechanical clamping with a separate seal (bonded washer, O-ring, gasket) on the face of the fitting. The threads do not seal. Thread interference (wedging action) between the male and female threads. The threads themselves form the primary seal.
ISO Standard ISO 228-1 ISO 7-1
Common Designations G (e.g., G 1/4) R (external taper), Rc (internal taper), Rp (internal parallel)
Sealant Requirement Not required for the threads. Seal is on the washer/gasket. Almost always required (PTFE tape, pipe dope) to fill helical leak paths.
Typical Applications Hydraulic systems, pneumatic connections, low-pressure plumbing, applications requiring repeated assembly/disassembly. General plumbing, gas lines, fire sprinkler systems, permanent installations where a robust, vibration-resistant seal is needed.

A Practical Guide: Identifying BSP Threads in Three Steps

Having established the theoretical framework, we now turn to the practical task of identification. You might be in a workshop in Dubai, a factory in Brazil, or a construction site in South Africa, faced with a pipe or fitting of unknown origin. How do you determine with certainty what it is? This three-step process will guide you.

Step 1: Visual Inspection – The Taper Test

The first and simplest step is to use your eyes. Pick up the male fitting and look at the threads from the side.

  • Do the threads appear straight and uniform from start to finish? If so, you are likely looking at a BSPP (G) thread. The overall shape of the threaded portion is cylindrical.
  • Do the threads appear to form a cone, getting smaller toward the end of the fitting? If so, you are likely looking at a BSPT (R) thread. The shape is conical.

For a female fitting, this can be more difficult to see. You can sometimes gauge the taper by looking into the port, but a more reliable method is to try threading in a known parallel male fitting. If it screws in a few turns and then stops abruptly, the female thread is likely tapered. If it screws in freely until the flange meets the port face, the female thread is likely parallel.

This initial visual check is a quick way to narrow down the possibilities by half. It is the fundamental branching point in the identification process.

Step 2: Measurement Mastery – Using Calipers and Gauges

If visual inspection is inconclusive, or if you need absolute certainty, it is time for precise measurement. You will need two basic tools: a thread pitch gauge and a set of calipers.

Measuring Thread Pitch

A thread pitch gauge is a tool with a series of blades, each with a specific thread profile cut into it. To measure the pitch, you simply try to match the blades against the threads of your fitting until you find one that sits perfectly within the threads with no gaps or rocking.

For BSP threads, the gauge will be marked in TPI (Threads Per Inch). Press the gauge blade against the threads and hold it up to a light source. If no light shines through between the gauge and the thread, you have found a perfect match. Read the TPI value stamped on the blade. BSP threads have a limited set of standard pitches (e.g., 28, 19, 14, 11 TPI), so this is a very strong identifying feature.

Measuring Thread Diameter

Next, use your calipers to measure the outside diameter (OD) of the male thread at its widest point (usually the first full thread). For a female thread, measure the inside diameter (ID) of the thread crests. It is good practice to take measurements at a few points around the circumference and average them to account for any slight ovality.

Be precise. Measure in either millimeters or inches, but be consistent. Record this measurement alongside the TPI you found. You now have two critical pieces of data: the thread pitch and the major diameter.

Step 3: The Chart Cross-Reference – From Measurement to Size

With your TPI and diameter measurements in hand, the final step is to compare them against a standard reference chart. This chart is the Rosetta Stone for what are BSP thread sizes, translating your physical measurements into the nominal size designation.

The table below provides the essential data for common BSP sizes.

Nominal Size (inch) Threads Per Inch (TPI) Pitch (mm) Male Thread OD (mm) Male Thread OD (inch)
1/8 28 0.907 9.73 0.383
1/4 19 1.337 13.16 0.518
3/8 19 1.337 16.66 0.656
1/2 14 1.814 20.96 0.825
5/8 14 1.814 22.91 0.902
3/4 14 1.814 26.44 1.041
1 11 2.309 33.25 1.309
1 1/4 11 2.309 41.91 1.650
1 1/2 11 2.309 47.80 1.882
2 11 2.309 59.61 2.347
2 1/2 11 2.309 75.18 2.960
3 11 2.309 87.88 3.460

How to Use the Chart: Let’s walk through an example. Suppose you have an unknown male fitting.

  1. Step 1 (Visual): You look at it and the threads appear parallel. You suspect it’s BSPP.
  2. Step 2 (Measurement): You take out your pitch gauge and find a perfect match with the “14 TPI” blade. You then use your calipers and measure the outside diameter as 26.4 mm.
  3. Step 3 (Cross-Reference): You look at the chart. You scan down the TPI column to “14”. You then look across that row at the “Male Thread OD (mm)” column. The value 26.44 mm is a very close match to your measurement of 26.4 mm. Following that row to the left, you find the nominal size: 3/4″.

You can now confidently identify your fitting as a G 3/4 (or BSPP 3/4″). This systematic process removes guesswork and ensures you select the correct mating part for a secure and leak-free connection.

Global Standards in Context: BSP vs. NPT – A Tale of Two Systems

In the globalized economy, equipment and components are sourced from all over the world. This often leads to a collision of standards. The most common alternative to BSP is the American National Pipe Thread (NPT). While they look similar to the untrained eye, they are fundamentally incompatible. Understanding their differences is not just a matter of technical curiosity; it is a critical safety issue. For a more detailed comparison, exploring the bspt pipe thread sizes can provide deeper insights.

The American Counterpart: National Pipe Thread (NPT)

NPT is the U.S. standard for tapered threads used on pipes and fittings. Like BSPT, it is designed to create a seal through thread interference. However, its design philosophy stems from a different historical lineage, the Sellers thread form, rather than the Whitworth form. This leads to crucial geometric differences.

Key Distinctions

There are two primary differences that make BSP and NPT incompatible:

  1. Thread Angle: As we’ve learned, BSP threads have a 55-degree included angle with rounded crests and roots. NPT threads, on the other hand, have a 60-degree included angle with flattened crests and roots. This 5-degree difference is the most significant reason for their incompatibility.
  2. Thread Pitch: For many sizes, the thread pitch (TPI) is also different. For example, a 1/2″ BSP thread has 14 TPI, and a 1/2″ NPT thread also has 14 TPI. They might seem compatible. However, a 1″ BSP thread has 11 TPI, while a 1″ NPT thread has 11.5 TPI.

The Perils of Mismatching

What happens when you try to connect a male NPT fitting to a female BSP port? The difference in thread angle and, in some cases, pitch prevents them from engaging properly. You might be able to screw them together for one or two turns, and they may even feel tight. This creates a false sense of security.

However, the threads are not properly seated. They are only making contact on a single point of the thread flank instead of across the entire surface. This connection has virtually no structural integrity and will not seal reliably under pressure. Applying torque in an attempt to force them together will result in a process called thread galling or cross-threading, permanently damaging both the male and female fittings.

In a low-pressure water line, this might result in a persistent, annoying leak. In a high-pressure hydraulic system or a critical fire protection pipe fitting application, this failure could be catastrophic, leading to equipment damage, production downtime, or severe personal injury. The rule is absolute: Never interchange BSP and NPT fittings.

Applications and Industries: Where BSP Threads Find Their Purpose

The prevalence of BSP threads across various industries speaks to their reliability and versatility. For professionals working in international markets, encountering these threads is a daily reality.

Fire Protection Systems

In the domain of fire safety, reliability is non-negotiable. Fire sprinkler systems, hydrants, and hose connections must function flawlessly when called upon. BSPT threads are widely used in these systems for their robust, vibration-resistant seals. The tapered design ensures a tight connection that is less likely to loosen over time, which is a vital quality for a system that sits dormant for long periods but must perform perfectly in an emergency. Leading manufacturers supply a range of grooved pipe fittings and fire valves that are compatible with BSP standards, often holding certifications from bodies like UL (Underwriters Laboratories) and FM (Factory Mutual) to guarantee their suitability for these life-safety applications.

Plumbing and Waterworks

BSP is the de facto standard for plumbing in much of the world outside North America. From the taps in your kitchen to the connections on your water heater, BSP threads are everywhere. BSPP (G) threads are often used for faucet connectors and flexible hoses, where the ability to easily assemble and disassemble the connection for maintenance is valued. The seal is made by a simple rubber washer. BSPT (R) threads are more common for fixed pipework, such as the main water lines running through a building, where a permanent and durable seal is the priority. Galvanized pipe fittings with BSP threads are common in water systems for their corrosion resistance.

HVAC and Pneumatics

In Heating, Ventilation, and Air Conditioning (HVAC) systems, as well as in pneumatic (compressed air) and hydraulic systems, BSP threads are extensively used. The high pressures involved in hydraulic systems make the sealing integrity of the connections paramount. BSPP fittings, when used with a high-quality bonded seal, provide an excellent sealing solution that is resistant to high pressures and vibration. They are found on pumps, cylinders, valves, and manifolds. In pneumatic systems, BSP threads connect everything from air compressors to the handheld tools on an assembly line.

The Global Marketplace Perspective

For businesses and engineers operating in the Middle East, Africa, South America, and Southeast Asia, a deep understanding of what are BSP thread sizes is an essential professional skill. These regions are often a crossroads of international trade, where equipment from Europe (predominantly BSP) might need to be integrated with systems from the United States (predominantly NPT) or Asia (which uses a mix of standards). Being able to correctly identify threads, specify the correct fittings, and understand the need for adapters is crucial for successful project execution. A knowledgeable supplier, such as Fire Protection Manufacturers, can be an invaluable partner in navigating these challenges, providing not just components but also the technical expertise to ensure system compatibility.

Advanced Considerations and Professional Practices

Mastery of BSP threads goes beyond simple identification. Professional installation and use require attention to detail regarding sealants, torque, and material selection.

The Role of Sealants and Tapes

The rule is straightforward:

  • BSPP (G) threads do not require sealant on the threads. The seal is made by the washer or O-ring. Applying sealant to the threads is unnecessary and can interfere with proper assembly. The only time a substance might be applied is a light lubricant to prevent galling on stainless steel fittings.
  • BSPT (R) threads almost always require a sealant. The sealant’s job is to fill the tiny helical gap at the crests and roots of the thread to ensure a 100% leak-proof joint. The most common sealant is PTFE tape. When applying PTFE tape, it should be wrapped clockwise (when viewed from the end of the fitting) on the male thread. This ensures that the tape does not unwrap as the fitting is tightened. Typically, 2-3 wraps are sufficient. Over-taping can be as bad as under-taping, as it can strain and even crack the female port. Liquid or paste-type sealants (pipe dope) are also effective and are often preferred in systems subject to high vibration.

Torque Specifications and Proper Tightening

Proper tightening is a balance. Under-tightening a BSPT fitting will result in a leak. Over-tightening can be even more destructive. For a tapered thread, excessive torque can create immense radial (hoop) stress in the female port, potentially causing it to crack, especially if it is made of a brittle material like cast iron. For a BSPP fitting, over-tightening can crush the bonded seal or gasket, destroying its ability to seal effectively.

While specific torque values depend on the size, material, and pressure rating, the general principle is to tighten to a “wrench-tight” feel. For BSPT, this typically means tightening by hand until snug, and then using a wrench for another one to two full turns. For BSPP, tighten until the seal is felt to compress, then give a final small turn to secure it. Always follow the manufacturer’s recommendations when they are available.

Material Choices: From Brass to Stainless Steel

The material of a fitting is chosen based on the application’s requirements for pressure, temperature, corrosion resistance, and fluid compatibility.

  • Brass: Common in general plumbing and low-pressure pneumatic applications. It is easy to machine and has decent corrosion resistance.
  • Steel and Malleable Iron: Strong and durable, suitable for high-pressure applications. They are often coated for corrosion protection. Common examples include black iron pipe fittings (coated with a black oxide layer) used in gas lines, and galvanized pipe fittings, which are coated with zinc for excellent corrosion resistance in water and outdoor applications.
  • Stainless Steel: Offers superior corrosion resistance and is essential for use in food processing, pharmaceutical, and marine environments. It is also suitable for high-pressure and high-temperature applications.
  • Plastic (e.g., PVC, Nylon): Used for low-pressure fluid applications where corrosion is a major concern.

Choosing the correct material is just as important as choosing the correct thread type for ensuring the long-term reliability of a piping system.

Frequently Asked Questions (FAQ)

Can I use a BSPP male fitting with a BSPT female port?

This is generally not recommended for a pressure-tight seal. While a parallel male thread can screw into a tapered female port, it will only engage on a few threads before it bottoms out or jams. It will not form a proper seal and is structurally weak. The only exception is when a BSPP male fitting is specifically designed with a tapered seat that can seal on the cone of a female BSPT port, but this is a specialized design.

Is a ‘G’ thread the same as BSPP?

Yes. ‘G’ is the international standard designation (ISO 228) for a parallel pipe thread. The term BSPP is the common industrial name. If you see a fitting marked G 1/2, it is a 1/2-inch British Standard Pipe Parallel thread.

How can I quickly tell if I have a BSP or NPT thread?

The two most reliable methods are checking the thread angle and the pitch. Use a thread gauge; NPT and BSP pitches differ for many sizes (e.g., 1″ NPT is 11.5 TPI, while 1″ BSP is 11 TPI). If the pitch is the same (e.g., 14 TPI for 1/2″ size), check the thread form. The 55° angle of BSP threads is visibly narrower than the 60° angle of NPT threads. The rounded crests of BSP are also a good indicator compared to the flattened crests of NPT.

What does the ‘R’ in R 1/4″ stand for?

The ‘R’ comes from the German word Rohr, meaning pipe. In the ISO 7 standard, ‘R’ specifically denotes an external (male) tapered pipe thread. An internal tapered thread would be ‘Rc’, and an internal parallel thread intended for sealing with an R male would be ‘Rp’.

Why is a 1″ BSP thread not actually 1 inch in diameter?

This is a historical convention. The nominal size (1″) refers to the approximate internal bore of the original pipe standard, not the outside diameter of the threads. The OD of a 1″ male BSP thread is significantly larger, about 1.309 inches or 33.25 mm. Always use a chart to convert your measured diameter to the correct nominal size.

Do all BSP threads need sealant?

No. This is a crucial distinction. Tapered (BSPT, R-series) threads require a sealant like PTFE tape or pipe dope to ensure a leak-free joint. Parallel (BSPP, G-series) threads do not; they seal using a bonded washer, O-ring, or gasket at the face of the fitting, and sealant on the threads is unnecessary.

What are the essential tools for identifying BSP thread sizes?

The two most important tools are a set of digital or dial calipers for accurately measuring the outside or inside diameter, and a thread pitch gauge (also called a screw pitch gauge) for determining the number of threads per inch (TPI). A good reference chart is the third essential “tool.”

Conclusion

The subject of what are BSP thread sizes, while seemingly technical and niche, forms a cornerstone of mechanical and fluid engineering across a vast portion of the globe. It is a language of connection, a grammar of pipes and fittings that ensures our systems for water, gas, and power function safely and reliably. We have journeyed from the historical imperative for standardization in Whitworth’s 19th-century workshop to the practical, hands-on process of identifying a thread in a modern industrial setting. The fundamental division between the parallel (BSPP) and tapered (BSPT) forms, their distinct sealing mechanisms, and their incompatibility with other standards like NPT are not just points of trivia; they are principles that prevent leaks, avert failures, and ensure operational integrity. By arming yourself with this knowledge—by learning to see the taper, to measure the pitch, and to consult the charts—you move from being a passive user of components to an informed practitioner, capable of making sound engineering judgments that contribute to safer and more efficient systems everywhere.

References

British Standards Institution. (2000). BS EN ISO 228-1:2003: Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions, tolerances and designation. BSI.

British Standards Institution. (2003). BS EN 10226-1:2004: Pipe threads where pressure tight joints are made on the threads — Part 1: Taper external threads and parallel internal threads. Dimensions, tolerances and designation. BSI.

Engineers Edge. (n.d.). British Standard Pipe (BSP) Thread Data. Retrieved January 15, 2025, from

International Organization for Standardization. (2000). ISO 228-1:2000: Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions, tolerances and designation. ISO.

International Organization for Standardization. (1994). ISO 7-1:1994: Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances and designation. ISO.

Machinery’s Handbook. (2020). British Standard Pipe Threads. In E. Oberg, F. D. Jones, H. L. Horton, H. H. Ryffel, & C. J. McCauley (Eds.), Machinery’s Handbook (31st ed., pp. 2097–2102). Industrial Press.

Parker Hannifin Corporation. (2017). Thread Identification Guide (Catalog 4400).

RYCO Hydraulics. (2022). RYCO Thread and Connector Identification Manual.

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