General > General Technical Chat
why is the US not Metric
KL27x:
--- Quote from: soldar on November 16, 2019, 08:08:13 pm ---
--- Quote from: vk6zgo on November 16, 2019, 12:24:07 pm ---They are commonly known as "AF"(across flats).
...
Metric spanners are "across flats", too, but we don't call them "AF".
--- End quote ---
Originally spanners/wrenches were denominated with the size of the thread, not by the size of the head. Then they realized it made more sense to use the size of the head "across flats".
Kind of the same thing with pipes. Nominal 1/2" pipe thread has a diameter of 0.8125" because the denomination is not the measure of the thread but of the inside diameter of the standard pipe with that thread. These days pipes walls are thinner so in a 1/2" pipe nothing measures 1/2".
--- End quote ---
The reason pipes still go by ID is because that's what you generally want to know about a pipe, to know how much volume or cross sectional area it has. If you need a precise standard size of OD, you need a "tube" not a "pipe." Tubes are made to and sold by their OD.
soldar:
--- Quote from: KL27x on November 16, 2019, 11:29:38 pm --- The reason pipes still go by ID is because that's what you generally want to know about a pipe, to know how much volume or cross sectional area it has.
--- End quote ---
Except, as I noted, nominal diameters are not actual diameters so your point is not valid. Furthermore, if you are talking about the thread you would be interested in, you know, the thread dimensions. I cannot see how the guy making the thread would be concerned with the water-carrying capacity of the pipe. Especially since you could have that thread on a solid rod or on a pipe with smaller inside diameter. The thread is named and defined by the name which has a very distant relation to how the name originated.
--- Quote from: KL27x on November 16, 2019, 11:29:38 pm --- If you need precise OD, you need a "tube" not a "pipe." Tubes are sold by their OD.
--- End quote ---
Let me repeat myself: So-called 1/2" pipe was denominated that way because it originally had that inside diameter but what was fixed was the outside diameter so it could take nominal 1/2" thread at the ends. When manufacturing methods allowed thinner walls the outside diameter was maintained (for obvious reasons) which meant a larger inside diameter.
Pipe thread names are not a definition of the actual dimensions of the thread, they are named like they are for historical reasons. That is the point I was trying to make.
Just like today they sell the new lightbulbs in "watts equivalence". They mark an LED bulb as "100 W" meaning it illuminates like an incandescent 100 W bulb.
KL27x:
--- Quote ---Pipe thread names are not a definition of the actual dimensions of the thread, they are named like they are for historical reasons. That is the point I was trying to make.
--- End quote ---
Ok. I completely missed that part about the threading.
But to anyone who is trying to build something without a full machine shop at hand, I hope my point was useful, nonetheless, about tube vs pipe. Maybe it is obvious to everyone else, but I didn't learn of the distinction until I actually needed to know. Also, I know exactly what you mean the distinction between precision and standardized size; see the timestamp on my last edit, strikethrough and italics. I think we're on the same page. I'm sorry for the confusion and thanks for the clarification.
Going back to pipe threads, in a way this is a constant problem I have when writing code. Not being omniscient, the labels I come up with very often do not stand up to the test of time. I'd do so far as to say, trying to name things in a logical way can take a lot of my time and effort.
tooki:
--- Quote from: KL27x on November 16, 2019, 06:46:06 pm ---America:
We know metric is better
--- Quote ---Here's another calculation to illustrate the point: a 400V 3 phase geared motor is 80% efficient. It lifts a 500lb weight, to a height of 12ft, in 30 seconds. Think about how you'd work out the power in metric (Watts) vs imperial (horsepower). Now calculate the current draw, assuming a power factor of 0.9. I'm not going to go through it, but to calculate the current you'll need power in Watts, a metric unit, so why not start with metric units in the first place? Try again with 227kg and 365.8m. See how much easier it is.
--- End quote ---
You know, America has heard of this thing called the watt. This is what we use for this for electronics. I'm sure your countries still use horsepower or CV to describe car engine power. So maybe you should tell yourself this.
The biggest problem for America is that if America ever (officially) changes to metric (not like it isn't already metric), there will be only 5000 Rowandans for us to feel smug and superior over. You guys seems to be really enjoying this (by giving so many examples that don't apply to us or to you or to 99% of average citizens).
Tooki:
--- Quote ---What makes you think that anyone outside the US (and possibly Canada, eh!) buys SAE sized tools? Every single tool I've bought since about 1981 has been metric sized. I say 1981 because I remember having to get some secondhand imperial sized tools back then to maintain an antediluvian AJS motorcycle that some of us were restoring.
--- End quote ---
I think all the people who complain about fastener sizes on this thread have had to do so at some point. Even you admit you haven't bought them because... you already own a set. :) I don't think this is going to change even if America were to change its road signs and speedometers and drivers licenses and for us to sell houses in square meters and for cops to call out APB on 20 yr old male, 1.68 meter, 70 kilo.
And I know you, Tooki, are not one of these guys. All of your posts are reasonable and practical. They know who they are. The ones making the imperial or dry gallon crack and such.
Re: fastener situation in America:
I'm not a mechanic or a machinist or a professional fabricator. When it comes to wrenches (spanners? I mean the bars of metal with the open end and the box end), I have only one set, and it is metric. I have lived here my entire life, and I have never purchased an SAE wrench. (Inexpensive sockets sets usually come with both, so that is all I have needed to date for SAE bolt, which is not common). This is all you need to work on most modern cars in the last 20 years (at least 20, which goes back before I started to do anything other than sit in class rooms and play computer games) as well as most power tools (that are pretty much 99.9999% imported). But, I have only SAE set of hex bits. I find that the closest torx bit usually works for metric hex fasteners.* And for some reason, I find hex screws are rather often SAE, even on imported tools. The metric hex fasteners is the odd duck in America, still, IMO. But that is just my single anecdote.
So Tooki, you are one up on me to even own a set of SAE wrenches. I have never.
*and if that doesn't work, a piece of hex bar and a belt sander will do the trick.
--- End quote ---
Thank you for the kind words, but actually you messed up the quoting a bit, because it wasn’t me who bought the SAE tools, that was the person I was quoting! :p
(I own a random mix of piecemeal hex sockets, bought as needed when living in USA or CH, so a mess I’m sure! OK, actually I think it’s mostly metric, but purely because of immediate need, not dogma.)
vk6zgo:
--- Quote from: KL27x on November 16, 2019, 06:46:06 pm ---America:
We know metric is better
--- Quote ---Here's another calculation to illustrate the point: a 400V 3 phase geared motor is 80% efficient. It lifts a 500lb weight, to a height of 12ft, in 30 seconds. Think about how you'd work out the power in metric (Watts) vs imperial (horsepower). Now calculate the current draw, assuming a power factor of 0.9. I'm not going to go through it, but to calculate the current you'll need power in Watts, a metric unit, so why not start with metric units in the first place? Try again with 227kg and 365.8m. See how much easier it is.
--- End quote ---
You know, America has heard of this thing called the watt. This is what we use for this for electronics. I'm sure your countries still use horsepower or CV to describe car engine power. So maybe you should tell yourself this.
The biggest problem for America is that if America ever (officially) changes to metric (not like it isn't already metric), there will be only 5000 Rowandans for us to feel smug and superior over. You guys seems to be really enjoying this (by giving so many examples that don't apply to us or to you or to 99% of average citizens).
Tooki:
--- Quote ---What makes you think that anyone outside the US (and possibly Canada, eh!) buys SAE sized tools? Every single tool I've bought since about 1981 has been metric sized. I say 1981 because I remember having to get some secondhand imperial sized tools back then to maintain an antediluvian AJS motorcycle that some of us were restoring.
--- End quote ---
I think all the people who complain about fastener sizes on this thread have had to do so at some point. Even you admit you haven't bought them because... you already own a set. :) I don't think this is going to change even if America were to change its road signs and speedometers and drivers licenses and for us to sell houses in square meters and for cops to call out APB on 20 yr old male, 1.68 meter, 70 kilo.
And I know you, Tooki, are not one of these guys. All of your posts are reasonable and practical. They know who they are. The ones making the imperial or dry gallon crack and such.
--- End quote ---
But that was you!
--- Quote ---Re: fastener situation in America:
I'm not a mechanic or a machinist or a professional fabricator. When it comes to wrenches (spanners? I mean the bars of metal with the open end and the box end), I have only one set, and it is metric. I have lived here my entire life, and I have never purchased an SAE wrench. (Inexpensive sockets sets usually come with both, so that is all I have needed to date for SAE bolt, which is not common). This is all you need to work on most modern cars in the last 20 years (at least 20, which goes back before I started to do anything other than sit in class rooms and play computer games) as well as most power tools (that are pretty much 99.9999% imported). But, I have only SAE set of hex bits. I find that the closest torx bit usually works for metric hex fasteners.* And for some reason, I find hex screws are rather often SAE, even on imported tools. The metric hex fasteners is the odd duck in America, still, IMO. But that is just my single anecdote.
So Tooki, you are one up on me to even own a set of SAE wrenches. I have never.
*and if that doesn't work, a piece of hex bar and a belt sander will do the trick.
--- End quote ---
The small sized metal threaded screws commonly used to assemble US made Electronic equipment seem to
have no equivalent in the Imperial range formerly used in Australia & the UK for the same purpose.
Woe betide anyone who loses a Screw when they dismantle a piece of Tektronix equipment.
Tek recognised this problem, & often supplied a bag with some spare screws for the outside cover.
If it is an inside screw you're on your own! ;D
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