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Thread: Differences in UK and US Inch?
08-02-2009, 02:05 PM #1
Differences in UK and US Inch?
I' justy been reading through some old Popular Mechanics magazines.
I was surprise to find a reference to different US and UK Inches (PM Feb '63 p58) "...the British gallon is slightly is slightly large than the US version but the inch is slightly smaller there than here."
I know the Inch as used here in the UK now is defined as 25.4mm, the same as the US inch but, has it ever been different?
08-02-2009, 02:25 PM #2
Before world or even national standards, there were all sorts of differences from place to place, and not just in the inch.
08-02-2009, 02:38 PM #3
The various inch standards converged on 25.4 mm in 1959 (ever wondered why the conversion is exactly at 25.4000?). The US inch changed slightly more than the British inch, but the differences are very small (millionths of an inch). Having said this it might matter if you were buying slip gauges that were from around this date.
I think the old inch standards are still in use for some purposes in the US - surveying?
08-02-2009, 02:41 PM #4
The US inch changed slightly more than the British inch,
08-02-2009, 03:05 PM #5
08-02-2009, 03:05 PM #6
Differences would have inevitably arisen between the inch standards in different places.
I don't know when the US Standard inch was adopted, but let's say it was the mid 19th century. There would have been no sophisticated techniques available to compare the length with some invariable property like the wavelength of something, or whatever is used nowadays.
No, you'd have to transfer measurements from an existing standard, using either an 'end' measurement (i.e. the measured length of a bar). or the length between lines engraved on a bar. In either case, there are limits to the accuracy of transferring these measurements, so inevitably differences would arise, especially with the equipment available at the time.
08-02-2009, 03:10 PM #7
08-02-2009, 03:27 PM #8
Theres a good article on Wikipedia: http://en.wikipedia.org/wiki/Foot_(length)
I'm fairly sure that in electronics drafting software such as Protel Autotrax the inch isn't 25.4mm based on dimensions from US component manufacturers but I can't find the reference article I read this on. It may just be an electronics only dimensional quirk.
Edit: I found the article here: http://users.tpg.com.au/rcspcb/quotepcb.txt and i include an excerpt from it below, keeping in mind this guy is referring to the 1950's :
"Many years ago, when I was working at a place in the states that made jet
aircraft, I was pulled up and questioned about the new emerging 'metric'
size and the new term was a millimetre. Now this was going to be to the
masses, Joe Public, an equivalent size known at 2.54mm per tenth of an
Well, I quickly learned that in aviation that measurement is NOT regarded
as correct; from memory it is 2.5367mm approx. So when you see in future,
measurements given in millimetres, bear in mind that they are approximate
'conversions'. Maybe they're near enough for cake making and decorating,
but not nearly accurate enough in precise engineering terms for serious
electronic equipment, jet turbines, lasers etc."
08-02-2009, 04:06 PM #9
08-02-2009, 04:08 PM #10
Aviation metics and imperial metric use the same conversion factors as other sectors of science and industry. "2.5367mm" does not equal 1/10" exactly. The offical and legal conversion from millimeter per inch equals 25.4mm per inch exactly. Used to be 39.37 inches per meter. There's about 0.000004" difference but that was changed in the metrification of US Customary Units effective July 1, 1959.
Units of length, mass, etc are matters of international treaty retified by Congress and implemented by the US Dept of Commerse and similar bodies all over the world.
Common, local, and customary usage are unoffical and do not contravene the Metric standard and the inch equivalency. These international standards don't affect customary and local units (Danish pounds and French tois for example) used every day.
There's hardly any other industry fussier over the standards they use than aviation. Nothing is left to chance and their calibration programs are second to none. If the metric standard for aviation was different from other sectors of world commerce and industry, there would be uproar and disorder sufficient for the world standards associations to petition their respective governments for instant resolution in the form of treaty amendments and UN actions in assembly.
Nope the inch equals eacty 25.4 mm.
08-02-2009, 04:24 PM #11
According to my calculator
1000 divided by 25.4 = 39.370078
39.370078 '' X 25.4 = 999.99998
That must be the millionths talked about.
08-02-2009, 04:38 PM #12
Could someone shoot the A hole who invented the inch system. 12 inches to a foot! makes perfect sense!
Could we also shoot the A holes who resisted converting to metric back in the 70's? Maybe it was the 50's, I can't remember.
I just don't understand how these ridiculous counting systems caught on.
08-02-2009, 05:04 PM #13
08-02-2009, 05:16 PM #14
Samy, you need a better calculator. Then you will be the answer you are SUPPOSED to get.
08-02-2009, 05:25 PM #1512 inches to a foot! makes perfect sense!
08-02-2009, 05:27 PM #16
some people don't like the metric system
08-02-2009, 05:47 PM #17
Having grown up using metric and decimals, it only recently (while using an imperial thread cutting lathe) that I've fully appreciated how easy it is to use fractional measurements.
Last edited by Billtodd; 08-02-2009 at 05:48 PM. Reason: must get a spool choaker for IE7
08-02-2009, 07:33 PM #18
If everyone in the world used the Metric system and all the machines were Metric it would be fine, but they're not.
I have Imperial machines so I use the Imperial system. I use .03937 as my conversion number and it works out close enough for me.
I would prefer the whole world used one system but it don't and someday maybe it will when we have one government and one system for everything.
I hope I'm gone way before then.
I think I read somewhere the military was the motivation at or before WWI to standardize sizes and measurements.
08-02-2009, 08:08 PM #19
What's the fuss? I've made metric stuff on Imperial machinery and Imperal stuff on Metric machines by most machining methods and variations thereof - ad nausium. A thread is a thread is a thread and measuring systems can be converted back and forth without end. So long as there are lazy people and calculators the machine intrinsic units can be used to make stuff to any units desired including femto parsec and RPH's.
It's all stuff and measuring units are all the same providing you got a calculator, a conversion table, slide rule, or logrithm. Done em all; so has everyone else in industry.
If you favor one unists system over the other fine but why resent the other? Each has advantages, just not the same advantages.
08-02-2009, 08:12 PM #20