NPT and BSP Thread Explained for Beginners and Professionals

When you work with piping systems, you need to choose the right pipe thread standards to avoid a costly leak or other issues. Each standard has different measurements and fits. If you use the wrong one, you risk damage or unsafe connections. You can learn to spot the differences and make better choices. Careful selection keeps your system safe and reliable.

Key Takeaways

• Understanding pipe thread types is crucial for creating secure connections. Identify the thread type before making any connections to avoid leaks.
• Different thread standards, like NPT and BSP, have unique angles and sealing methods. Always check compatibility to prevent costly mistakes.
• Use reference tables and tools to measure diameter, pitch, and angle accurately. Proper identification ensures safe and leak-free connections.
• Select the right thread standard based on your application’s pressure, temperature, and fluid type. This choice enhances system reliability and safety.
• Always follow safety practices when working with pipe threads. Wear protective equipment and conduct risk assessments to prevent accidents.

What is Type Threads?

When you work with pipes, you often hear the word type. You need to know what type threads mean before you choose fittings or make connections. Type threads describe the shape, size, and pattern of the grooves cut into the ends of pipes or fittings. Each type helps you create a secure joint that can handle pressure and prevent leaks.

You find many type threads in plumbing, gas, and hydraulic systems. Some type threads seal by squeezing together. Others use a gasket or sealant. You must match the type to your system for safety and reliability.

Major engineering standards organizations define type threads in specific ways. The table below shows how ISO and ANSI describe type threads:

Standard	Description
ISO 7	Defines pipe threads where pressure-tight joints are made on the threads, including taper external threads and parallel internal threads.
ANSI	Covers American National Standard Pipe Thread standards, which include both tapered and straight thread series for various applications, ensuring rigidity and pressure-tight sealing.

You see that each standard uses type threads for different purposes. ISO 7 focuses on pressure-tight joints. ANSI covers both tapered and straight type threads for many uses.

When you look at a pipe, you notice the type by checking the angle, pitch, and diameter of the threads. You also see if the type is tapered or straight. Tapered type threads get tighter as you screw them together. Straight type threads stay the same width along their length.

You should always identify the type before you connect pipes. If you mix the wrong type, you risk leaks or damage. You can use reference charts or thread gauges to check the type. Many professionals mark the type on fittings to help you choose the right one.

To sum up, type threads are the patterns that let you join pipes safely. You need to understand each type to build strong, leak-free systems. When you know the type, you make better choices and avoid costly mistakes.

Thread Type	Description	Characteristics	Applications
NPT	Tapered thread, according to U.S. standard	60-degree thread angle, seals through taper	Piping connections for gas, liquid, and oil in the U.S. and Canada
BSP	British Standard Pipe thread, includes BSPT (tapered) and BSPP (parallel)	55-degree thread angle; BSPT seals through taper, BSPP requires washers or O-rings for sealing	Piping systems in Europe, Asia, and Australia
Metric	Metric system threads, available in coarse (M) and fine (MF) pitches	60-degree thread angle, typically requires washers or O-rings for sealing	Global applications in engineering, machinery, automotive, and construction
SAE	Society of Automotive Engineers standard threads	Internal taper thread with 45-degree angle; straight threads require O-rings for sealing	Hydraulic, automotive, and refrigeration systems in North America
JIS	Japanese Industrial Standard threads, similar to BSP threads	55-degree thread angle; seals through taper or additional sealing elements	Various piping systems in Japan

Common Pipe Thread Standards Overview

When you work with pipe thread standards, you need to know the most common thread types. Each standard has unique features, regions of use, and applications. Understanding these thread standards helps you choose the right fittings and avoid leaks.

NPT Threads

NPT threads stand for National Pipe Taper. You find npt threads mostly in the United States and nearby regions. NPT thread uses a 60° angle and a tapered design. This taper helps create a tight seal when you use a sealant. NPT thread standards work well in plumbing, gas, and hydraulic systems. You see npt thread in high-pressure applications. NPT threads do not fit with bsp thread or metric thread types.

Dash Size (Nominal Size)	Thread Pitch	Male Thread O.D.mm	Male Thread O.D.inches	Female Thread I.D.mm	Female Thread I.D.inches
-02(1/8)	27	10.3	0.41	9.40	0.37
-04(1/4)	18	13.7	0.54	12.4	0.49
-06(3/8)	18	17.3	0.68	15.7	0.62
-08(1/2)	14	21.3	0.84	19.3	0.76
-10(5/8)	14	22.9	0.90	21.1	0.83
-12(3/4)	14	26.9	1.06	24.9	0.98
-16(1)	11 1/2	33.3	1.31	31.5	1.24
-20(1 1/4)	11 1/2	42.2	1.66	40.1	1.58
-24(1 1/2)	11 1/2	48.3	1.90	46.2	1.82
-32(2)	11 1/2	60.4	2.38	57.9	2.29

Tip: NPT threads were first established in the U.S. in 1864 by William Sellers.

BSP Threads

BSP threads, or British Standard Pipe, include bspt threads and bspp threads. BSPT stands for British Standard Pipe Taper, while BSPP means British Standard Pipe Parallel. BSP thread uses a 55° angle. You find bsp thread in Europe, Australia, and many Asian countries. BSPT threads seal by taper, while bspp threads need a gasket or O-ring. BSP thread standards are common in plumbing, gas, and industrial systems. BSPT threads and bspp threads do not mix with npt thread.

Dash Size (Nominal Size)	Thread Pitch	Male Thread O.D.mm	Male Thread O.D.inches	Female Thread I.D.mm	Female Thread I.D.inches
-02(1/8)	28	9.7	0.38	8.9	0.35
-04(1/4)	19	13.2	0.52	11.9	0.47
-06(3/8)	19	16.5	0.65	15.2	0.6
-08(1/2)	14	20.8	0.82	19.1	0.75
-10(5/8)	14	22.4	0.88	20.3	0.8
-12(3/4)	14	26.4	1.04	24.6	0.97
-16(1)	11	33	1.3	31	1.22
-20(11/4)	11	41.9	1.65	39.6	1.56
-24(11/2)	11	47.8	1.88	45.5	1.79
-32(2)	11	59.7	2.35	57.4	2.26

Metric Threads

Metric thread types use millimeter measurements. You see metric threads in Europe, Asia, and worldwide. Metric threads have a 60° angle. These thread types often need a gasket or O-ring for sealing. Metric thread standards appear in automotive, hydraulic, and industrial machinery. Metric threads do not match npt or bsp thread.

Metric Threads Chart

SI Metric Port Size mm	Thrcad Pitch (mm)	Male Thread O.D   (mm)	Male Thread O.D (inches)	Female Thread I.D (mm)	Female Thread I.D (inches)
M8 X1.0	l	8	0.315	6.9	0.272
M10X 1.0	1	10	0.394	8.9	0.35
M10X1.5	1.5	10	0.394	8.4	0.331
M12X 1.0	l	12	0.472	10.9	0.429
M12X1.5	1.5	12	0.472	10.4	0.409
M14X1.5	1.5	14	0.551	12.4	0.488
M16X 1.5	1.5	16	0.63	14.4	0.567
M18X1.5	1.5	18	0.709	16.4	0.646
M20X1.5	1.5	20	0.787	18.4	0.724
M22X1.5	1.5	22	0.866	20.4	0.803
M24X1.5	1.5	24	0.945	22.4	0.882
M26X1.5	1.5	26	1.024	24.4	0.961
M27X2.0	2	27	1.063	24.8	0.976
M30X2.0	2	30	1.181	27.8	1.094
M33X2.0	2	33	1.299	30.8	1.213
M36X2.0	2	36	1.417	33.8	1.331
M42X2.0	2	42	1.654	39.8	1.567
M45X2.0	2	45	1.772	42.8	1.685
M48X2.0	2	48	1.89	45.8	1.803
M52X2.0	2	52	2.047	49.8	1.96
M60X2.0	2	60	2.362	57.8	2.276

SAE Threads

SAE threads come from the Society of Automotive Engineers. SAE thread types use a 45° or straight thread. You find sae threads in North America, especially in automotive and hydraulic systems. SAE threads often need O-rings or gaskets for sealing. SAE thread standards do not fit with metric, npt, or bsp thread.

SAE Thread Chart

Dash Size (Nominal  Size)	Thread Pitch	Male Thread O.D.mm	Male Thread O.D.inches	Female Thread I.D.mm	Female Thread I.D.inches
-02(1/8)	24	3.9	0.31	6.9	0.27
-03(3/16)	24	9.6	0.38	8.6	0.34
-04(1/4)	20	11.2	0.44	9.9	0.39
-05(5/16)	20	12.7	0.5	11.4	0.45
-06(3/8)	18	14.2	0.56	12.9	0.51
-08(1/2)	16	19	0.75	17	0.67
-10(5/8)	14	22.3	0.88	20.3	0.8
-12(3/4)	12	26.9	1.06	24.9	0.98
– 14(7/8)	12	30	1.18	27.7	1.09
– 16(1)	12	33.3	1.31	31	1.22
– 20(11/4)	12	41.4	1.63	39.1	1.54
-24(11/2)	12	47.7	1.88	45.5	1.79
-32(2）	12	63.5	2.5	61.2	2.41

JIS Threads

JIS threads follow the Japanese Industrial Standard. JIS thread types look similar to bsp thread, using both parallel and tapered designs. JIS threads use a 55° angle. You find jis threads in Japan and some Asian countries. JIS thread standards appear in automotive, hydraulic, and industrial equipment. JIS threads have limited compatibility with bsp thread but do not fit npt thread.

JIS Thread Chart

Dash Size (Nominal Size)	Thread Pitch	Male Thread O.D.mm	Male Thread O.D.inches	FemaleThread I.D.mm	Female Thread I.D.inches
-02(1/8)	28	9.4	0.37	8.1	0.32
-04(1/4)	19	13.7	0.53	12.4	0.49
-06(3/8)	19	17.2	0.68	16	0.62
-08(1/2)	14	21.5	0.84	19.8	0.77
-10(5/8)	14	23.1	0.91	20.6	0.81
-12(3/4)	14	26.9	1.06	25.4	1
-16(1)	11	34	1.34	31.8	1.25
-20(11/4)	11	42.6	1.68	40.4	1.59
-24(11/2)	11	48.5	1.9	46.2	1.81
-32(2)	11	60.4	2.37	58.2	2.29

Other Types

You may also see ISO thread standards. ISO thread types can be tapered or parallel. ISO thread standards are recognized worldwide and adapt to many applications. Some systems use custom or less common thread types, but you should always check compatibility.

Comparison Table of Common Thread Types

Thread Standard	Thread Type	Angle	Sealing Method	Regions of Use	Typical Applications
NPT	Tapered	60°	Thread engagement with sealant	United States, North America	Plumbing, gas, hydraulics
BSPT	Tapered	55°	Thread engagement with sealant	Europe, Asia, Australia	Plumbing, gas, industry
BSPP	Parallel	55°	O-ring or gasket	Europe, globally	Industrial, pneumatic
Metric	Parallel	60°	O-ring or gasket	Europe, Asia, globally	Automotive, machinery
SAE	Straight/45°	45°/Straight	O-ring or gasket	North America	Automotive, hydraulics
JIS	Parallel/Tapered	55°	O-ring, gasket, or thread engagement	Japan, Asia	Automotive, machinery

Note: Always check the thread angle, type, and sealing method before connecting different thread standards.

You now have a clear overview of the most common pipe thread standards. This knowledge helps you select the right thread types for your system and avoid costly mistakes.

Key Differences

When you compare pipe thread standards, you notice several key differences that affect how pipes fit and seal. Understanding these differences helps you choose the right threads for your project.

Thread Angles

Thread angle is the shape of the thread’s peak and valley. Each standard uses a different angle. For example, NPT and Metric threads have a 60° angle, while BSP and JIS use a 55° angle. SAE threads use a 45° angle. These angles change how threads fit together and seal. If you mix threads with different angles, you risk leaks or poor connections.

Thread Type	Thread Angle	Compatibility Issues
NPT	60°	Not compatible with BSP due to different angles
BSP	55°	Not compatible with NPT
JIS	55°	May match BSP dimensions but follows different standards
SAE	45°	Compatibility varies based on connection type
Metric	60°	Does not match any imperial thread standards

Note: Even a small difference in angle can prevent a tight seal.

Tapered vs Parallel

Pipe threads come in two main shapes: tapered and parallel. Tapered threads, like NPT and BSPT, get tighter as you screw them together. This wedging action helps create a seal and adds strength. Parallel threads, such as BSPP and Metric, stay the same width along their length. They need extra parts like O-rings or gaskets to seal.

Thread Type	Sealing Mechanism	Mechanical Strength
Tapered Threads	Seal as threads wedge together; need sealants	Good for high-pressure systems
Parallel Threads	Need O-rings or gaskets for sealing	Used in moderate to low-pressure systems

Sealing Methods

You find two main ways to seal pipe threads. Tapered threads seal by squeezing together, often with a thread sealant. This method works well for high-pressure systems. Parallel threads need a gasket or O-ring to stop leaks. You must pick the right sealing method for your system’s pressure and fluid type.

• Tapered threads create a seal through interference fit.
• Parallel threads depend on external sealing components.
• Using the wrong method can cause leaks or system failure.

Regional Use

Different regions prefer different thread standards. The United States uses NPT threads and focuses on detailed documentation. The UK prefers BSP threads and values traceability. Asian countries use a mix of standards and offer competitive pricing. These regional choices affect how you source parts and ensure quality.

Region	Quality Control Focus	Compliance Requirements	Supplier Selection Risks
USA	Detailed documentation	Deeply rooted in production	Vet factories, ask for MTRs
UK	Heavy emphasis on traceability	Extra paperwork, third-party verification	Vet factories, ask for MTRs
Asia	Scale and competitive pricing	Produces ASME/EN-spec fittings	Use third-party testing for compliance

Tip: Always check the thread standard used in your region before ordering parts.

By learning these key differences, you can avoid mismatched threads and build safer, more reliable piping systems.

Thread Compatibility

When you work with piping, you must understand thread compatibility. Not all pipe thread standards fit together. If you mix the wrong threads, you risk leaks, damage, and system failure. You need to know which threads can connect and when you need adapters.

NPT vs BSP

NPT and BSP threads look similar, but they have important differences. NPT uses a 60° thread angle and a tapered design. BSP threads use a 55° angle and come in both tapered (BSPT) and parallel (BSPP) forms. You cannot connect NPT and BSP threads directly. The angles and profiles do not match. If you force these threads together, you can strip the threads and weaken the joint. This mistake often leads to leaks and pressure loss in piping systems. In pressurized systems, this can cause serious failures and safety hazards.

You must use proper adapters if you need to join NPT and BSP threads. These adapters match the thread profiles and angles, creating a safe and leak-free connection. Always check the thread type before making any connection. If you see NPT and BSP fittings, do not mix them without an adapter.

⚠️ Mixing NPT and BSP threads without adapters can lead to leaks, stripped threads, and system failure. Always use the correct adapter for safe compatibility.

Metric vs Imperial

Metric threads use millimeter measurements. Imperial threads, such as NPT and BSP, use inch-based measurements. You cannot connect metric and imperial threads directly. The pitch, diameter, and angle differ. If you try to force a metric fitting onto an imperial thread, you risk damaging both parts. This mistake can cause leaks and reduce the strength of your piping system.

You need special adapters to connect metric and imperial threads. These adapters match the measurements and profiles, allowing you to join different standards safely. Always measure the thread diameter and pitch before choosing an adapter. If you work with international piping systems, keep metric and imperial adapters on hand.

Tip: Metric and imperial threads have different measurement systems. Use adapters to ensure compatibility and prevent leaks.

Adapters

Adapters help you solve compatibility challenges in piping. You use adapters when you need to connect different pipe thread standards. Adapters come in many shapes and sizes. Some match NPT to BSP. Others join metric to imperial threads. You must choose the right adapter for your system’s pressure and temperature needs.

Here is a table showing common adapter limitations:

Limitation	Description
Compatibility Issues	BSP adapters may not fit properly with NPT threads due to differences in thread profiles, pitch, and taper angles, leading to potential leaks.
Pressure and Temperature Limits	BSP adapters have specific operational limits; exceeding these can cause failure due to material properties.
Sealing Challenges	While BSPT adapters are designed for self-sealing, improper tightening or debris can still lead to leaks.
Limited Design Flexibility	Standard sizes may not meet all project requirements, necessitating custom designs for unique systems.
Corrosion and Wear	Exposure to corrosive environments can lead to issues like dezincification in brass adapters, compromising their integrity over time.

You must check the adapter’s specifications before use. If you work with high-pressure or hazardous piping, consult a professional. Some adapters may not handle extreme conditions. Always follow industry guidelines for safety.

• Leak Prevention: Proper sealing is crucial to avoid leaks, especially under high pressure, which can occur with mismatched threads like NPT and BSPT.
• Durability Under Stress: Threads that meet specific standards ensure connections can endure mechanical and thermal stress without failure.
• Regulatory Compliance: Many regulations require adherence to recognized thread standards to ensure safety and environmental protection.

If you face complex compatibility challenges, ask a professional for advice. High-pressure and hazardous systems need expert guidance. You protect your piping system and avoid costly mistakes by following best practices.

Note: Always use reference tables and consult professionals when working with unfamiliar pipe thread standards or high-pressure piping systems.

Thread Identification

You need to identify pipe threads accurately to ensure safe and leak-free connections. If you misidentify a thread, you risk leaks, system failures, and costly downtime. You can use several practical steps and tools to make sure you select the correct thread type every time.

Measure Diameter

Start by measuring the outside diameter of the thread. Use a micrometer or caliper for precise results. Place the tool across the widest part of the thread and record the value. You may see measurements in inches or millimeters, depending on the standard. For example, a 1/4-inch pipe thread has an actual outside diameter of 0.54 inches.

Nominal Size	Actual OD	Hand Tight Turns	Wrench Turns
1/8	0.405 inches	4.5	2.5
1/4	0.54 inches	4	3
1	1.32 inches	4.5	3.25

Tip: Always measure the widest part of the thread for the most accurate result. Incorrect measurement can lead to incomplete engagement and poor sealing.

Check Pitch

Next, check the pitch of the thread. Pitch means the number of threads per inch or the distance between threads. Use a pitch gauge or a ruler to count the threads. Place the gauge against the thread and match the teeth to the grooves. If you use a ruler, count the number of threads in one inch. This step helps you match the thread to the correct standard.

1. Use a pitch gauge for best accuracy.
2. Count the threads per inch or measure the distance between threads.
3. Compare your results to reference tables for npt, BSP, or metric threads.

Note: If you miscount the pitch, you may select the wrong fitting and cause leaks or thread stripping.

Identify Angle

You need to identify the angle of the thread. Most pipe threads use either a 60-degree or 55-degree angle. NPT threads use a 60-degree angle, while BSP threads use a 55-degree angle. You can use a thread profile gauge or compare the thread visually to a known sample. The angle affects how the threads fit and seal.

• NPT: 60-degree angle, common in North America.
• BSP: 55-degree angle, used internationally.
• SAE: 45-degree angle, found in automotive systems.

Tip: Even a small difference in angle can prevent a tight seal and lead to leaks.

Tapered or Parallel

Determine if the thread is tapered or parallel. Tapered threads get tighter as you screw them together. Parallel threads stay the same width along their length. You can check this by looking at the thread profile or measuring the diameter at different points.

• Tapered threads seal by wedging together, often with sealant.
• Parallel threads need a gasket or O-ring for sealing.

If you mix tapered and parallel threads, you risk poor sealing surfaces and system failure under pressure.

Markings

Look for markings on the pipe fitting. Manufacturers often stamp or engrave codes to indicate thread type and size. Common markings include NPT, BSPT, GHT, NST, and NPSM. These markings help you quickly identify the standard and select the right fitting.

Thread Type	Characteristics	Applications
NPT	Tapered threads with a 60-degree angle	General purposes, low pressure air or liquids
NPTF	Tapered threads designed to seal mechanically	Applications with higher heat or pressure
BSPT	55-degree thread angle	International standard for joining steel pipes
GHT	Coarse threads for hoses	Quick attachment of hoses to valves
NST	Coarse threads for hoses	Quick attachment of fire hoses to valves
NPSM	Straight threads requiring a washer or gasket	Joining applications only

Tip: Always check for markings before making a connection. Markings reduce the risk of mismatched threads and help you follow safety standards.

Reference Tables

Use reference tables to confirm your measurements and thread identification. Major standards organizations like ANSI, ISO, and JIS provide tables that list thread types, sizes, and descriptions. These tables help you match your measured diameter and pitch to the correct thread standard.

Standard	Type of Thread	Description
ANSI	NPT	National Pipe Thread, tapered threads for leak-tight seals.
ISO	ISO 7-1	International standard for tapered threads, similar to NPT.
JIS	JIS B0203	Japanese standard for tapered threads, comparable to ISO and ANSI.
	ISO 228-1	International standard for parallel threads, similar to NPS.
	NPS	National Pipe Straight, used for fastening connections without leak-tight seals.

Note: Reference tables are essential for confirming thread type and avoiding costly mistakes. Always compare your measurements to the tables before making a final selection.

You can follow these steps to identify pipe threads with confidence. Accurate identification prevents leaks, improves safety, and saves time in the workshop or field.

Thread Selection Tips

Application Match

You should always match the pipe thread standard to your specific application. Each system has unique needs. For example, high-pressure or high-temperature environments require threads that can handle stress and prevent leaks. The type of fluid, such as water, oil, or chemicals, also affects your choice. Some fluids need special materials or thread designs to avoid contamination or corrosion. The table below shows important factors to consider:

Factor	Description
Pressure	Prevent leaks under high pressure.
Temperature	Ensure performance in extreme heat or cold.
Fluid Type	Choose threads that resist corrosion or contamination.
Industry Needs	Meet hygiene or vibration resistance for your industry.
Risk Level	Use threaded or non-threaded designs based on sensitivity of the system.

Tip: Always review your system’s pressure, temperature, and fluid type before selecting a thread standard for your application.

Regional Standards

You need to check which thread standards are common in your region. North America often uses NPT, while Europe and many other countries use BSP. Using the local standard makes it easier to find compatible parts and reduces the risk of mismatched connections. If you work on international projects, keep adapters handy for different standards.

Standardization

Standardizing pipe thread selection within your organization or project brings many benefits. You reduce the chance of mismatched parts and make maintenance easier. The table below highlights key benefits:

Benefit	Description
Compatibility	Ensures all parts fit together, even from different suppliers.
Reliability	Increases system reliability over time.
Cost Savings	Lowers installation and maintenance costs.

Note: Standardization helps you avoid confusion and keeps your system running smoothly.

Safety Advice

You must follow safety practices when handling and installing pipe threads, especially in high-pressure systems. Here are some important steps:

• Wear personal protective equipment (PPE) during installation.
• Check for hazards and review safety data sheets for all materials.
• Align pipes carefully to prevent leaks or bursts.
• Secure pipes during transport to avoid damage.
• Test the system after installation and stand clear during pressure testing.

Always conduct a risk assessment before starting work. Proper safety steps protect you and your system from accidents.

You play a key role in keeping piping systems safe and reliable. When you identify and select pipe thread standards correctly, you avoid leak risks and prevent costly issues. Always use reference tables and seek expert advice for complex jobs.

• Learn to spot different thread types for secure connections.
• Apply sealants properly to stop leaks.
• Inspect threads visually before making a choice.
• Choose the right thread and sealant to protect your system.

More information about Type Threads:

FAQ

What is the main difference between NPT and BSP threads?

You will notice that npt threads use a 60-degree angle and a tapered design. BSP threads use a 55-degree angle and can be either tapered or parallel. You cannot connect npt and BSP threads directly because their shapes do not match.

Can you use NPT fittings with metric threads?

You cannot use npt fittings with metric threads. The measurements, angles, and pitches differ. If you try to connect them, you risk leaks or damage. Always use the correct adapter when you need to join npt and metric systems.

How do you identify an NPT thread?

You can identify an npt thread by checking for a 60-degree angle and a tapered profile. Measure the outside diameter and count the threads per inch. Look for markings like “NPT” on the fitting to confirm the standard.

Why do NPT threads need sealant?

Npt threads need sealant because the tapered design alone does not guarantee a leak-proof seal. You should apply thread sealant or tape to fill small gaps and prevent leaks, especially in high-pressure systems.

What happens if you mix NPT and BSP threads?

If you mix npt and BSP threads, you risk leaks, stripped threads, and system failure. The angles and profiles do not match. Always use the correct adapter or matching thread standard for a safe and reliable connection.