Thursday, February 19, 2009

British Standard Pipe Threads

Greetings from Diane, whose duty it is today to speak of British Standard Pipe Threads. You can’t tell on the web page, but I’m using my fake British accent as I type this. In fact, chums, this thread type has been adopted around the world as a standard for mating external and internal threads, and are common outside the U.S.

The two types of BSP threads are BSPT (British Standard Pipe Taper) and BSPP (British Standard Pipe Parallel). BSPT threads have a diameter that increases or decreases along the length of the thread. On the other hand, BSPP threads have a constant diameter.

For your enlightenment, blokes, here’s one of our GN 743.6 fluid level sight glasses that happens to be available in BSPP thread versions.

These two types of threads can be used to achieve two types of jolly good, never-wonky joints:

Joining threads joints: A taper male thread is used, in conjunction with either a taper or parallel female thread. The combination creates a pressure-tight joint.

Longscrew thread joints: In this case, parallel pipe threads are used, and the tightness of the joint is achieved by some sort of sealing ring (washer or O-ring) between the end face of the male thread and a socket or nipple face, incorporating the tightening of a backnut.

And while I’m getting really technical (well, for me), I’ll mention that BSP threads use the Whitworth threadform. Quite! That means:

--a symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)

--truncation at top and bottom of one-sixth of this sharp V

--threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks

--the theoretical depth of the thread is therefore 0.64 times the nominal pitch

I know that all sounded especially impressive in this British accent I’m using.

You’ll find tables with all the specs for BSP thread on our Web site in the Technical Section here: British Standard Pipe Threads You might want to bookmark that page. I know how much engineers fancy it because it’s consistently in the top ten entry pages on our site and people find it via Google every day.

Which is why I can make the claim that our BSP tables are smashing, the dog’s bollocks, and absolutely take the biscuit.

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