# name and source for a threaded adapter...killing me! **URL:** \ **Category:** Factual Questions\ **Created:** [February 10, 2017, 12:35pm UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455 "2017-02-10T12:35:47Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![PoppaSan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/poppasan/32/189_2.png) [@PoppaSan](https://boards.straightdope.com/u/PoppaSan)\ **Post date:** [February 17, 2017, 1:19am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/21 "2017-02-17T01:19:05Z")
> [@SigMan](#): > > 1/2" = 12.7mm to be precise. 1/2" and 13mm wrenches can be interchangable. Until your 13mm wrench rounds the corners of the really tight hex nut because close enough wasn’t. ---
**Author:** ![Richox](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@Richox](https://boards.straightdope.com/u/Richox)\ **Post date:** [February 18, 2017, 1:38am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/22 "2017-02-18T01:38:48Z")
> [@ZurBob](#): > > Uhhh, OK…:rolleyes: How did your test go? failed at the certification stage, unfortunately. ---
**Author:** ![ZurBob](https://avatars.discourse-cdn.com/v4/letter/z/71e660/32.png) [@ZurBob](https://boards.straightdope.com/u/ZurBob)\ **Post date:** [February 18, 2017, 5:38am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/23 "2017-02-18T05:38:36Z")
Out of curiosity, what fitting did you utilize, and what aspect about it failed? I assume you determined the necessary thread type beforehand: BSP vs NPT? ---
**Author:** ![Richox](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@Richox](https://boards.straightdope.com/u/Richox)\ **Post date:** [February 18, 2017, 10:31am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/24 "2017-02-18T10:31:37Z")
A direct fitting as could be found upthread - essentially a threaded coupler, 20mm M to 15mm F. No common or standardized name identified. I assuredly know the difference between BSP and NPT. NPT is my only interest - I referred to BSP in the OP because i wanted to broaden the question to the entire range of common thread types. In case it was a common thing in BSP but not in NPT, etc etc. The standard I am working within only allows an \*upright \*sprinkler to have a 15mm size connection. A pendant sprinkler - which is my interest in this application - of the size I need to use (K11.2/ K160) requires a 20mm thread minimum. I cannot determine why this is, but must accept it as a basic fact unfortunately. ---
**Author:** ![ZurBob](https://avatars.discourse-cdn.com/v4/letter/z/71e660/32.png) [@ZurBob](https://boards.straightdope.com/u/ZurBob)\ **Post date:** [February 21, 2017, 7:04am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/25 "2017-02-21T07:04:00Z")
> [@Richox](#): > > I assuredly know the difference between BSP and NPT. NPT is my only interest Your initial post stated: “Thread types are all BSP or NPT, can’t recall at the moment.” So it is not unreasonable to question your knowledge of such.:mad: They are obvious in their difference. It is difficult to imagine, irrespective of thread type, that any fire pipe retrofit cannot be amended by the proper application of a pipe threader and a few common "T"s, "El"s, and adapters. What’s the big deal? ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [February 21, 2017, 8:52am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/26 "2017-02-21T08:52:47Z")
> [@Richox](#): > > Yeh everyone in the metric world knows 1"=25.4mm, however a 1/2" fitting it called a 15mm fitting colloquially. Additionally, the actual thread OD measures something like 20mm at the narrowest anyway, so the whole convention is a mess already haha. Not just colloquially. It’s the ASME B36.10 standard ‘Diametre Nominal’. It is, I think, the metric standard (metric pipe standardization was very strange). The 1/2" is the nominal /inside/ diameter, and 1/2" pipe is of course, “Pipe that has the same outside dimension as nominal 1/2” pipe had when they standardized pipe sizes". Since pipe wall thickness is thinner now than it was when 1/2" nominal pipe was invented, pipes that have the same /outside/ diameter as nominal 1/2" pipe now have /more/ than 1/2" inside diameter. 15mm. Except that 15mm pipes come in a selection of inside diameters, so most (??) 15mm pipe will not have a 15mm inside diameter either. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [February 21, 2017, 8:57am UTC](https://boards.straightdope.com/t/name-and-source-for-a-threaded-adapter-killing-me/779455/27 "2017-02-21T08:57:45Z")
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