The plumbing threads used in the United Kingdom (UK) and the United States of America (USA) are not identical, and care should be taken when connecting pipes and fittings from different countries.

In the UK, plumbing threads are known as British Standard Pipe threads (BSP). These threads have a tapered design, which means that the diameter of the thread gets smaller as it goes deeper into the fitting. This creates a tighter seal as the pipe is screwed in further. BSP threads come in two types: BSPP (parallel) and BSPT (tapered). The BSPP threads are typically used on pipe fittings that are screwed together, while the BSPT threads are used on pipe fittings that are screwed into a female fitting.

In the USA, plumbing threads are known as National Pipe Thread (NPT) threads. These threads are also tapered, but the taper is much less pronounced than the BSP threads. This means that the NPT threads don’t create as tight of a seal as the BSP threads. NPT threads are typically used in the USA for pipe fittings that are screwed into a female fitting.

When connecting pipes and fittings from different countries, it is important to ensure that the threads are properly matched. Connecting a BSP fitting to an NPT pipe, for example, will create a leaky connection, as the threads are not compatible. Adapters are available to connect pipes and fittings with different thread types, but it is important to ensure that the adapter is rated for the pressure and temperature of the application.

In summary, plumbing threads used in the UK and the USA are not identical, UK use BSP threads while USA use NPT threads. BSP threads are tapered and create a tighter seal while NPT threads are less pronounced and do not create as tight of a seal. It’s important to ensure proper compatibility when connecting pipes and fittings from different countries, and adapters are available but should be used carefully.
Another important thing to consider when connecting pipes and fittings from different countries is the measurement units used. In the UK and most of Europe, plumbing measurements are typically given in metric units (millimeters and centimeters). However, in the USA, plumbing measurements are typically given in imperial units (inches and feet). So, when connecting pipes and fittings from the UK and the USA, it is important to be aware of the different measurement units used, and to use appropriate conversion factors.

Another thing to consider is the pressure rating, BSP and NPT threads have different pressure rating, BSP threads are rated for higher pressure than NPT threads. It’s important to ensure that the pressure rating of the fitting and pipe is compatible.

In addition, BSP and NPT threads are not the only standards out there, there are other standards such as ISO, JIS, and DIN etc. It’s important to check the standard of the fittings before connecting them to avoid any leaks or damage.

In conclusion, while plumbing threads used in the UK and the USA are not identical, it is possible to connect pipes and fittings from different countries with the use of adapters. However, it is important to be aware of the different thread types, measurement units, pressure rating, and standards used in different countries, and to take appropriate precautions to ensure a leak-free connection.