3/8 BSP thread characteristics and application

3/8 BSP thread (British Standard Pipe) is one of the most commonly used pipe threads in power hydraulics and pneumatics. The BSP designation indicates a British standard where the thread pitch is specified as the number of threads per inch, and its profile has an angle of 55°. In the case of 3/8 BSP thread, the outer diameter is approximately 16.3–16.6 mm, and the thread pitch is 19 threads per inch (3/8” – 19). BSP threads come in two versions: BSPP (parallel) – straight and BSPT (tapered) – conical. The 3/8 BSP thread in the BSPP version is particularly popular in fittings hydraulic, which require tightness thanks to sealing rings or copper washers. In turn, BSPT is used where tightness is achieved thanks to a tapered thread fit.

3/8 inch BSP thread dimensions

The 3/8” designation refers to the nominal pipe size, not directly to the outer diameter of the thread. In the case of 3/8 BSP thread the actual outer diameter is approximately 16.66 mm, while the number of threads is 19 per inch, which corresponds to a pitch of about 1.337 mm. These parameters comply with the British Standard Pipe standard and are crucial for the correct identification of hydraulic installation components. In practice, mistakes often occur during thread identification because the outer diameter of a 3/8 inch thread is not 9.5 mm, as a conversion of the inch value might suggest. Therefore, when measuring, always check the actual diameter and thread pitch using a gauge or thread recognition table.

3/8 BSP thread difference between BSPP and BSPT

The 3/8 inch BSP thread comes in two basic varieties: as a parallel thread BSPP designated by the symbol G 3/8 and as a tapered thread BSPT designated by the symbol R 3/8. In power hydraulics, the BSPP thread is much more commonly encountered, which is sealed with a bonded seal, O-ring or front-face seal. In the case of BSPT thread, sealing occurs on the thread taper by its wedging in the socket. This type of solution is used more often in water and gas installations than in precise power hydraulic systems operating under high pressure. The distinction between BSPP and BSPT is crucial for maintaining connection tightness. Using the wrong type of thread can lead to leaks, damage to the component, and loss of pressure in the installation.

Where is the 3/8 inch BSP thread used

3/8 BSP thread is widely used in fittings hydraulic, elbows, tees, quick couplings, valves ball valves and manometers. It very often appears as a connection thread in medium-diameter hydraulic lines and in control elements of hydraulic systems. In agricultural, construction, and industrial machinery, the 3/8 inch thread is a popular port size in auxiliary installations, supply lines, and lubrication systems. Due to its versatility, it is a standard in many industrial applications. Hydron offers hydraulic fittings with 3/8 inch BSP thread in various configurations, both as external and internal threads. This includes couplings, elbows, tees, reductions, and adapters enabling connections with other thread systems.

How to correctly measure a 3/8 inch thread

To correctly identify a 3/8 inch BSP thread, measure the outer diameter of the thread using a caliper and check the number of threads per inch using a thread gauge. It is worth remembering that BSP threads have a 55-degree profile angle, which distinguishes them from NPT threads which have a 60-degree angle. A diameter measurement of approximately 16.6 mm and 19 threads per inch confirms that we are dealing with a 3/8 BSP thread. In case of doubt, a thread selection table available in the Hydron store is helpful, allowing for a quick comparison of parameters.

3/8 BSP thread vs other thread systems

In power hydraulics, metric threads are also common, NPT and JIC. 3/8 BSP thread is not compatible with 3/8 NPT thread, despite the similar nominal designation. The differences concern the profile angle, taper, and sealing method. Attempting to connect these systems without an appropriate reduction can lead to thread damage and leaks. Therefore, in professional hydraulic installations, you should always precisely determine the thread type before assembling the components.

3/8 inch BSP thread in Hydron's offer

Hydron offers elements with 3/8 inch BSP thread intended for professional power hydraulics applications. We offer fittings, reductions, elbows, tees, quick couplings and connection elements made of high-quality materials, adapted to work under pressure. Thanks to many years of experience in the power hydraulics industry, we provide technical support in identifying threads and selecting the appropriate components. If you are not sure whether the element you have is a 3/8 BSP thread, we invite you to contact our team. We will help you choose the right solution and ensure the safe operation of your installation.

We invite you to familiarize yourself with the full range of inch threads in the Hydron store and to contact us for professional assistance.

Application of 3/8 BSP thread:

• hydraulic hose and line connections,

• hydraulic and pneumatic fitting components,

• quick couplings and adapters,

• reductions and adapters from other thread types (e.g., metric or inch),

• installation plugs and caps.

In power hydraulics, the 3/8 BSP thread is often found in medium flow cross-section components used in systems with operating pressures up to several hundred bar. It enables the mounting of elements with 3/8 BSP external threads into sockets or couplings with 3/8 BSP internal threads.

Smaller thread: 1/4 BSP
Larger thread: 1/2 BSP

In the offer of Hydron you will find a wide selection of connectors, ends and adapters with 3/8 BSP thread, available in straight, elbow, and tee versions, made of high-grade galvanized steel. All products meet the requirements for tightness and durability in high-pressure hydraulic systems.

3/8 inch BSP thread FAQ

What are the dimensions of a 3/8 inch BSP thread?

The 3/8 inch BSP thread has an outer diameter of approximately 16.66 mm and 19 threads per inch, which corresponds to a pitch of about 1.337 mm. These parameters comply with the British Standard Pipe standard and allow for correct thread identification in power hydraulic installations.

Is 3/8 BSP thread the same as 3/8 NPT?

No, 3/8 BSP thread differs from 3/8 NPT in profile angle and sealing method. BSP thread has a 55-degree angle, while NPT has a 60-degree angle and is a tapered thread. These two systems are not directly compatible and require an appropriate reduction.

What is the difference between 3/8 BSPP and 3/8 BSPT?

3/8 BSPP thread is a parallel thread and is sealed with a washer, O-ring, or face seal. 3/8 BSPT thread is tapered and seals by wedging the thread in the socket. In power hydraulics, the BSPP variant is more commonly used.

Where is the 3/8 inch BSP thread used?

3/8 inch BSP thread is used in hydraulic fittings, elbows, tees, manometers, and connection elements in power hydraulic installations. It is a popular size in agricultural, industrial, and construction machinery.

How to correctly measure a 3/8 inch thread?

To confirm that it is a 3/8 BSP thread, measure the outer diameter of the thread, which should be approximately 16.6 mm, and check the number of threads per inch using a thread gauge. If in doubt, it is worth comparing the results with a thread recognition table.