BSP stands for ‘British Standard Pipe’ threads. BSP is the most popular thread style in the United Kingdom and is very common in the UK commonwealth countries. They are also widely used for many applications in Europe and Asia. BSP male fittings have a conical 30-degree seat that mates against matching conical 30-degree female fitting or port. BSP fittings have a thread angle of 55 degrees and come in two thread types:
Make sure to avoid the common mistake of confusing a BSP thread of 55 degrees with an American NPT (National Pipe Taper) of a 60-degree angle. BSP have rounded peaks and valleys, while NPT have flattened peaks and valleys. They may seem to fit, but the difference in thread angle and style will allow for leaking down the threads. When in doubt, verify the style with a thread gauge.
To measure a BSP and BSPP fitting, first determine the thread size:
Because BSPT fittings are tapered, the process for measuring them is different from that of BSPP. The BSPT outer diameter varies on the taper, so the above formula is not as accurate. Instead of beginning by measuring the outer diameter, first determine the fitting’s inner diameter by taking a calliper reading from inside its bore. Once determining the ID of the bore, reference the table to find the external thread dimensions.
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