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Comment by Animats | Hacker News Reader

Detroit is mostly metric. Many US-built cars use all metric fasteners. For export, you have to use metric fasteners, because few outside the US have inch-sized tools. Imported cars are, of course, all metric. Aviation is mostly metric for the same reason. DoD is metric to be compatible with NATO.

Housing, however, hasn't converted at all. Building dimensions, HVAC and plumbing in the US are still on inch units.

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...few outside the US have inch-sized tools.

An interesting frustration I've found in working with an immigrant friend: even though most of the fasteners we're turning are "imperial", he simply can't use imperial wrenches, because they require a familiarity with fractions. I'm fine with moving from half-inch to nine-sixteenths when the wrench is a bit too tight to fit, and frankly at this point I can usually tell the difference by eye before even opening the toolbox. OTOH my friend just goes from 13mm to 14mm to 15mm, ruining nuts and bolt-heads in the process.

Since tools should work for people rather than the other way around, one must conclude that metric-sized fasteners are superior to imperial-sized ones. It does seem odd that imperial fasteners were never sized by e.g. the twentieth of an inch, since that would have solved this problem completely.

Which is sad because the original complaint was they didn't want to switch because they'd need to replace their imperial tools. Joke's now on whoever said that, because it worked: now they need two sets of tools.

The humble 2x4 piece of lumber will likely be the last major industrial component to change over in the US.

Which actually measures 1-1/2" by 3-1/2", but let's not go there...

But will it?

In the UK 2x4, 2x2 etc is still commonly available, but it's 50x100mm. Probably has been for 30 years but only sold as 50x100 for ten or less. Metricating timber was easy because no one's going to notice or care if they get 25mm instead of each inch.

Metals, fastenings, pipes etc converted much slower because metric was often incompatible sizes without adapters.

> Which actually measures 1-1/2" by 3-1/2",

Isn't that because it's 2x4 before planing. cut lumber would be actually 2x4.

> Isn't that because it's 2x4 before planing. cut lumber would be actually 2x4.

It used to be, but now we're more efficient in our rough cutting and a 2x4 you buy was never actually a full 2x4.

And cut lengths of timber and sheet materials are usually multiples of 30cm but many people will order "8 foot" rather than 2.4m. Likewise joist and stud centres. However you can also get 3m or 5m, for example. Of course, most houses in the UK were built pre-metric system, so rooms will mostly be sized in feet, if they are in round units at all.

That actually raises an interesting question, what are dimensional lumber measurements like in metric?

Or do countries that use the SI system generally not use wood for framing?

In Canada we still use imperial for construction stuff, I guess for import/export reasons.

Oh and Farenheit for water and cooking temperatures. No idea why because I have no freaking idea what a Farenheit is otherwise.

And even then, it can vary by +/- 1/8". (I don't know if this is due to shrinkage from drying, or if they are deliberately milling it smaller to get more linear feet.)

More than that. It's 2x4 when cut wet, but shrinks to 1-1/2 x 3-1/2 when dry(er). Note that it will continue to grow and shrink over its life as humidity changes.

I don't try to figure out their fake dimensions; I just measure and buy what fits.

Oh, and this is why composites like MDF and plywood are better sometimes.

In reverse, in Europe measuring pipes ( or tools for them) diameter in inches is quite normal and ubiquitous. In oil business a lot of stuff is also measured in imperial units.

Let's not forget the monitor screen sizes. You can only get it in inches, so pretty every IT guy has a rough idea of how much is 14" and so on.

Yeah, the monitor one is a farce when you don't know aspect ratio though. And at some point the arguments over resolution start and then it gets truly awful. Monitors have scared me.

Except France, where even monitors and TVs are measured in cm.

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