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Comment by topazas | Hacker News Reader

Awesome, but what does 1'' mean? Some weird measurement unit?

That would be 2.54 times 1/100th of the distance light travels in a vacuum during 1/299,792,458 of the time it takes for 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of a cesium-133 atom, if you prefer.

Wrong!

While there is a 1 inch measure in common use that is as you described, the subject here is EMT. There is no dimension in EMT that is 1 inch by the system you describe. The diameter is close to 1 inch, but it is noticeably different to the naked eye, and for all useful purposes different enough that anything actually 1 inch in diameter is not compatible.

27 mm outside diameter. Which has zero relation to any other inch you might have heard of in common use (ie in the US).

" is imperial inches, ' is imperial feet.

It's awesome that they combine 1" pipe with a 5 mm hex [1] (often "Allen" in the US) fastener. :)

[1]: https://en.wikipedia.org/wiki/Hex_key

You see a lot of this in the bicycle industry. There are a lot of older standards in use like 9/16” pedal threads, 1 1/8” steerer tubes or 1” (25.4mm) handlebars but any new standard is metric - so bottom brackets, wheels, newer seat post diameters are all metric. It can make for some very strange looking spec sheets.

The actual size is 27mm. If you convert to an imperial system the size is not a nice number.

/s might have been needed, it appears.

1" is one inch

1' is one foot

So yeah, a weird measurement unit. Technically the symbol to be used is a prime symbol (https://en.m.wikipedia.org/wiki/Prime_(symbol)), but what’s used in practice is anything that looks close enough.

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