Comment by analog31 | Hacker News Reader

Comment by analog31 | Hacker News Reader

Parent Full thread

I work for a company that makes scientific equipment. We apply a few basic criteria, which narrow things down a lot.

First, a lot of those fasteners are either really specialized or just rare or obsolete. So they can be ruled out.

We look for something that will be easy for our assemblers, and for our field service technicians. They have given us feedback on what they like and dislike, including what kinds of tools are common in different parts of the world. They hate flat head screws. Hex socket screws are really easy, and it's also easy to make them look nice on an assembly.

To an increasing extent, we want tools that can be used with a torque handle. For instance hex drive is better than Philips in that regard.

I hate to say that it's still a work in progress, but we are heroically trying to get away from fractional drivers, especially for our field technicians who presently have to carry full sets of US and metric tools. We even have mixtures of US and metric in some products!

If something is meant to be serviced by a customer (e.g., a lamp or filter that gets replaced), then we stick with Philips, which we are told is common worldwide. Or we use a captive knurled fastener if it's in a place where there's finger access.

So these are just a few thoughts. Other considerations are whether you're in an industry that has already standardized on a particular tool set, such as metric allen wrenches for bikes.

> They hate flat head screws

My experience with flat head screws in a production environment was the driver slipping out of the screw and scratching the paint on the part being assembled. Boo!

My experience with Philips is, works great as long as people use the exact correct driver, which they won't. Which results in a striped screw and a striped driver. The latter like a bad penny will go on to strip more screws till someone holy and wise (me) tosses it in the dumpster.

So Flat, just don't. Philips is okay for light duty. Anything else use a Torx or Hex.

> We even have mixtures of US and metric in some products!

In North America, tire sizes are given in millimeter width, but imperial mounting diameter. E.g. 175-65R14: 175mm width, 65% aspect ratio (sidewall height to width or something like that), for a 14" wheel.

I just learned about Nominal Pipe Size, in which the number that precedes the word "inches" does not refer to any actual measurement on the pipe. The specific characteristic of the gas grill pipe hookup on the back of my house that makes it a "half inch pipe" is that it has a .84 inch outer diameter; there is literally nothing about it, including the inner diameter, that could be described by the words "half inch".

https://en.wikipedia.org/wiki/Nominal_Pipe_Size

Then of course there's North American dimensional lumber, where the actual dimensions are either 1/4, 1/2, or 3/4 inches less than the nominal dimensions. A 2x4 is 1.5 x 3.5 inches.

Basically people using numbers as symbols. Quite annoying.

The history is a little more interesting than that:

> Lumber's nominal dimensions are larger than the actual standard dimensions of finished lumber. Historically, the nominal dimensions were the size of the green (not dried), rough (unfinished) boards that eventually became smaller finished lumber through drying and planing (to smooth the wood). Today, the standards specify the final finished dimensions and the mill cuts the logs to whatever size it needs to achieve those final dimensions. Typically, that rough cut is smaller than the nominal dimensions because modern technology makes it possible and it uses the logs more efficiently. For example, a "2×4" board historically started out as a green, rough board actually 2 by 4 inches (51 mm × 102 mm). After drying and planing, it would be smaller, by a nonstandard amount. Today, a "2×4" board starts out as something smaller than 2 inches by 4 inches and not specified by standards, and after drying and planing is reliably 1½ by 3½ inches (38 mm × 89 mm).

https://en.wikipedia.org/wiki/Lumber#North_American_softwood...

It seems bizarre to me to define the standard 'size' of an item based on some aspect of the manufacturing process that is not part of the final product the user will ever see, or could measure.

Shoe sizes often measure the size of the last, not the foot. One shoe company I've bought from in the past had a warning on their webpage that they use different manufacturing processes for different models, so the same numbered size of two similar-looking shoes actually differ by quite a bit.

I also find shoe numbering bizarre. How could such a numbering system survive to this day? Why not use goddamn centimeters?

(Fortunately, e-stores selling shoes were bitten enough by the ridiculousness of that problem that they ended up providing scales translating shoe numbers to centimeters.)

Ultimately, the best workaround I've seen was the one the father of my SO used - he would measure the foot of his child, then cut a wooden stick to appropriate length, and go with that stick to the shoes store.

US shoe numbering for men is simple.

There is a bit of insanity in that women's and children's sizes are derived from that in more than one way.

There are two ways of determining size, but they are supposed to coincide, theoretically.

Manufacturers use the "last length" as the basis for shoe size. However, that is not the foot length, and how a shoe with a given "last length" fits a given foot is a variable and so the fit ultimately requires testing. The last length is supposed to be about two shoe sizes larger than the foot length.

The last length formula is L3 - 24. So a last length of 12 inches (one foot) corresponds to size 12. From there, surrounding sizes are 1/3 of an inch increments. Which is the odd thing: where else you do you see increments of 1/3 inch?

Thus, in any case, if you have a 12" foot, that's a US men's size 14.

The foot measuring instrument you see in stores, Brannock's Device, accounts for this and so its formula is L3 - 22.

So these sizing systems are intended to coincide, but are different estimators.

You can see that using centimeters doesn't solve all the problems. Suppose centimeters were used, but the manufacturers used last-length centimeters rather than foot centimeters. You'd have to convert your foot length to last length according to some rule of thumb, and then ultimately resolve things by trying the shoe. If manufacturers had to use foot centimeters, they wouldn't be able to measure some trivial property of the shoe like last size to determine size. Foot centimeters aren't absolute; they would have to use some representative model of a foot and base it off that: still no guarantee that a 27cm size based on a representative model foot fits your 27cm foot.

I own two pairs of men's boots, from different companies, with US sizes on the label 2.5 apart from each other. They're the same physical size, and both fit me perfectly. That's pretty typical. I generally have to try new shoes in about a 3-size range.

According to the L x 3 - 24 rule, these boot should be nearly an inch different (or at least, their lasts). Maybe the US system is theoretically simple, but in practice it seems to be just an arbitrary number that can't be meaningfully compared to anything except the same model of shoe from the same company.

In contrast, I've ordered shoes from Japan 3 times, from 3 different companies, and I did it by putting a ruler next to my foot, and then choosing that number of centimeters in the online form. Every time, I got a shoe that fits great.

Maybe using an absolute length doesn't solve all problems, but my experience (with sample size of probably N<20) is that it works far better in practice. An arbitrary unit of measurement removes accountability, by way of obfuscation, and gains us nothing.

Yeah, I meant "foot centimeters" - the issue isn't about metric vs. imperial, I'm just writing from European experience. The issue is about "foot" vs "last" vs "shoe numbers".

I'm not fully convinced by the argument that manufacturers (or at least distributors) can't use foot centimeters - after all, somehow I can successfully buy shoes on-line by measuring my foot and then using vendor-provided foot-length-to-shoe-size conversion scale to pick appropriate size. From the experience of myself and everyone else I asked around, this works reliably.

Added: for the people who - like me - have no damn clue what the hell "last" is, it's that wooden foot look-alike they use in shoemaking/repairing.

https://en.wikipedia.org/wiki/Last

Like a 4.5" so-called six inch sandwich at Subway.

Hot Tip

A foot long flat bread is actually longer than 12in.

Read that somewhere.

http://time.com/money/4079569/subway-footlong-lawsuit-12-inc...

But it's equivalent (in terms of capacity and robustness) to all other half inch pipes, the first of which had a half inch diameter. Or something like that - the Wikipedia page is complicated.

In some ways that's more useful. If you're designing a gas pipe for a house you probably care more about "how much gas can I get through this pipe" and "what is the failure rate" than "will I be able to fit it through a 0.83 inch hole".

It's annoying that "half inch" etc were the terms co-opted here instead of, say, "a level 4 pipe". But there is some reason for it.

No it isn't equivalent to all other pipes in terms of capacity and robustness. It is equivalent to the COMMON pipe today, but you still have to watch because some applications use the same thread/outside diameter but the walls are thicker. Also there are still some old pipes out there that really do have the 1/2 inch inside diameter, they are equivalent in terms of robustness, but obviously not capacity.

Of course I'm being pedantic - in reality you will probably never encounter the exceptions.

Is it correct to say it's equivalent or better than the "standard" half inch pipe in all three of: inside diameter (larger is better), outside diameter (smaller is better) and robustness? With the "standard" half inch pipe actually being an old type that is now obsolete?

Being pedantic again, there are cases where more inside diameter is not better. Some chemicals are unstable and dangerous when concentrated into too much volume: by increasing the inside diameter you make them more likely to explode. (acetylene - C2H2 - is the only one I can think of where this could matter). On the same lines, if the pipe is subject to heat/flame there is another case where modern metals might be worse by allowing thinner walls.

Again, this is only pedantic. In the unlikely event that the above matters you need a professional engineer (a legal term) to specify the exact properties of the pipe.

True for pvc pipes also. Quite confusing.

That's not even a North America only thing, as far as I know the format mm-%R/D" (175-65R14) is used universal. Of course only vintage cars have diagonal tires now so you will probably not see a tire with D

Can confirm: Car and motorcycle tires are measured in inch diameter, bicycle tires are measured in inch circumference.

I noticed that the other day too! Dumb question but what does the rest of the world do? Do they convert inches to mm or is the inches diameter just an approximation of the more exact metric diameters?

I can't speak for cars, but there's a similar situation with bicycle wheels and tires. There are all sorts of historical measures, such as "26 inch" and "700c," but at the same time most rims and tires are marked with ISO dimensions that are in mm and quite well defined.

So for instance my "27 x 1-1/8" tires are also ISO 28-630, where 28 is the approximate inflated width, and 630 is a particular dimension of the rim. When I buy a new tire, I look at the ISO number to make sure I got the right size.

I recently restored an old Schwinn with its own oddball tire diameter, but ISO numbers published by modern tire makers got me up and running with new tires.

I think that in a lot of cases, English vs metric is a moot point because a tool is so specialized (spark plug wrench) or because production tools are computerized and switch unit systems as needed. On a milling machine, all dimensions boil down to the number of stripes on a precision glass scale, regardless of what units you choose to specify.

Historically, there are bike parts with mm diameter and English thread pitch, such as some old French pedals.

Reply on news.ycombinator.com