British Metric Threads: What You Should Know

Hydraulic hoses are all about fit. A fitting that does not match the others can lead to leaks and damage to your equipment, and this means that you have to know which type of metrics your fittings use.

There is a good chance that some of your hose uses British metric threads. Fortunately, these are relatively easy to understand.

What Are British Metric Threads?

Engineering relies heavily on people using an agreed upon measurement and standard for their products. One internationally adopted technical standard for screw threads is called the British Standard Pipe. It is used for sealing and interconnecting pipes and fittings, as well as plumbing. Screw threads that meet this standard work through fitting an external thread (called the male thread) over an internal (called the female) thread.

Fittings with these types of threads are common in equipment that is made in Europe, though you can find plenty in the US too.

Thread Types?

These threads come in two types. There are parallel threads, where they stay the same width throughout the product, and there are tapering threads, which change size, either increasing or decreasing along their length. The tapering ones are indicated with an ‘R,’ and the parallel ones are indicated by a ‘G.’

You will often see the parallel threads called British Standard Pipe Parallel, or BSPP, and the tapered threads called British Standard Pipe Tapered, or BSPT.

Male BSPP can fit female BSPT so long as the female thread doesn’t turn. The shape of the end of the female thread prohibits them from fitting otherwise.

The BSPT can look a lot like another fitting type called the NPT. However, the British ones have a 55 degree thread flank angle, where the NPT threads have a 60 degree angle.

Both types of threads can then be used in jointing threads and longscrew threads. Longscrew threads squeeze something between the surface of the male thread and a socket surface. Jointing just mates two threads.

The Sizes

British metric threads come in at least 41 sizes from 1/16 to 18. They were named from the inner diameter of the screw, as measured in inches, but this does not reflect the names anymore because modern manufacturers frequently make them with thinner sides.

Identifying their size requires measuring the outer diameter of the thread in inches and then subtracting a quarter inch, and then counting how many threads per inch there are. You can then cross-reference it with a chart of British metric sizes.

Custom Hose Can Help You With British Standard Pipe Fittings

Since British metric is an international standard, they are widely recognized and there is a fair chance at least some of your equipment uses them. This is why Custom Hose carries British Flatface thread types, and we have years of experience that allows us to identify when it is being used and what size is being used in your equipment. This means that we will be able to:

  • Replace a worn fitting during preventative maintenance.
  • Provide bin-filling.
  • Fix a hose with these fittings at our store or through our mobile service.
  • Use this type of fitting in customized hose builds.

Our walk-in stores in Bloomington and Rochester carry this metric for fittings and hydraulic hose, and we have a fleet of trucks that can come out to your business to fit your hose on-site if you are in the Twin Cities area. We are even going to expand our on-site services to Rochester soon.

We have many other metrics and pride ourselves on our ability to service hydraulic hoses of all types, so if your hydraulic hose needs parts, repair, or maintenance, contact us. 

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