Hello Forum,

I have been trying to figure out the mathematical / geometric relations for a BSP and Metric. So far i nailed the metric, but the BSP is still bothering me, so maybe someone can help me.

British Standard Pipe - Wikipedia

From this article the pitch is written as decimal number, but the mathematical relation is 25,4/TPI, e.g 2,309 for TPI=11

When searching google for information regarding BSP the taper is for instance often denoted as 1° 47' = 1,78 (rounded). But the mathematical precise relation is a right triangle with height 16 and width 0,5.

When drawing a triangle with base 25,4/11 = 2,309 and angle 55° between the to remaining sides (See image) you get a height which you can calculate.

I found that 4*H/6 times 2 is the precise difference between D Major and D minor from the wiki article.

But then comes the actual diameter. For instance 1" is 33,249 which is very weird number which I cannot, for the love of god, find any reason for.

Can anybody help me figure this out?

Imperial Pipe size. OD fixed, ID depends on wall thickness or 'schedule'.

Size are ID of pipe, roughly.

That's why they make taper thread, OD ID doesn't matter. Just thread it pass OD and ID.

I don't think they round the threads.

Also look at NPT, similar design.