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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 c

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

golem14 8y ago
True for pvc pipes also. Quite confusing.
anamexis 8y ago
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.
- deleted 8y ago
  [deleted]
- TeMPOraL 8y ago
  Basically people using numbers as symbols. Quite annoying.
  - grzm 8y ago
    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_softwoods https://en.wikipedia.org/wiki/Lumber#North_American_softwood...
    - ken 8y ago
      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.
      - TeMPOraL 8y ago
        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.
        kazinator 8y ago
        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.
  - kazinator 8y ago
    Like a 4.5" so-called six inch sandwich at Subway.
    - nasredin 8y ago
      Hot Tip A foot long flat bread is actually longer than 12in. Read that somewhere.
      - kazinator 8y ago
        http://time.com/money/4079569/subway-footlong-lawsuit-12-inches/ http://time.com/money/4079569/subway-footlong-lawsuit-12-inc...
dmurray 8y ago
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.
- bluGill 8y ago
  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.
  - dmurray 8y ago
    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?
    - bluGill 8y ago
      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.

golem14 8y ago

True for pvc pipes also. Quite confusing.

anamexis 8y ago

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.

deleted 8y ago
[deleted]
TeMPOraL 8y ago
Basically people using numbers as symbols. Quite annoying.
- grzm 8y ago
  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_softwoods https://en.wikipedia.org/wiki/Lumber#North_American_softwood...
  - ken 8y ago
    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.
    - TeMPOraL 8y ago
      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.
      - kazinator 8y ago
        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.
- kazinator 8y ago
  Like a 4.5" so-called six inch sandwich at Subway.
  - nasredin 8y ago
    Hot Tip A foot long flat bread is actually longer than 12in. Read that somewhere.
    - kazinator 8y ago
      http://time.com/money/4079569/subway-footlong-lawsuit-12-inches/ http://time.com/money/4079569/subway-footlong-lawsuit-12-inc...

dmurray 8y ago

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.

bluGill 8y ago
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.
- dmurray 8y ago
  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?
  - bluGill 8y ago
    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.