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(OP)
Well I know how to read a micrometer very well, my question is on how to say the readings you get.

You learn at an early age the following (this part makes sense to me, both how you say it and its mathematical representation):

10      = tens place
1       = ones place
.1      = tenths place                = 1/10
.01     = hundredths place            = 1/100
.001    = thousandths place           = 1/1,000
.0001   = ten-thousandths place       = 1/10,000
.00001  = hundred-thousandths place   = 1/100,000
.000001 = millionths place            = 1/1,000,000

BUT, i am confused about how i hear people "saying" micrometer readings, they dont seem to reflect the above  (1" micrometer)

.1      = hundred-thousandths of an inch ?
.01     = ten-thousandths of an inch?
.001    = one-thousandths of an inch?
.0001   = tenths of an inch? also heard ten-thousandths??
.00001  = ten-millionths of an inch?
.000001 = millionths of an inch -or- microinch?

some of these i may have listed incorrectly, thats what i need help with.

Thanks

a "micro" is 1/1,000,000. So, a microMETER is one millionth of a METER. The confusion comes from using inches instead of international standards...

sanbas,

I have heard various ways of communicating fractional measurements.  It may be regional habit or a trait within a particular industry.  The variation in the way values are communicated is considerably less when using the metric system (though still there).

.1 inch could be said to either be a tenth of an inch, point one inches or one hundred-thousandths of an inch.

I think it is a human tendency to try to put whole numbers onto variables and hence we end up sliding or scaling the unit of measure accordingly.  For example for me, rob768's post on 1/1,000,000 of a meter to me is not one millionth of a meter, or even a thousandth of a millimeter, it just sounds more appropriate to use micron.

Regards,

Sanbas,

For the second case in your query, it comes, from what I can gather, is that in most US machine shops people get used to working on the 1/1000th  inch scale.  Most drawings that I have seen usually have dimensions that are like .01" +/-.005". or something like that.  Its just easier to say, "10 thou +/- 5 thou," with the thou being left out if people are feeling really lazy.  Correspondingly, .001" +/-.0005" would be, "One thou +/- 5 tenths."  Expect to see the decimal reference slide up and down, and adjust your fractions accordingly if you work in fields that require to be more or less accurate.

(OP)
is there a website available that explains the appropriate way to say these dimensions.  I have looked but have been unable to find it.

still a little confused on the different ways people say it,  My shop only uses english units (inches) and rarely do we use fractions, its exclusively in decimals.

sanbas,

This is simple mathematics (no offense meant).  The number 0.1 (inch, mile, whatever) can be read as "zero point one" or "one tenth" or "ten hundredths" or "one hundred thousandths" or ... ad infinitum.

rob768,

While I share your desire to use metric units exclusively, your post is nonsensical on this subject.  The word micrometer has two meanings: 1) unit of measure equal to one millionth of a meter or 2) a u-shaped device used to measure dimensions of an object (like thickness).  In this case, we are concerned with definition 2.

PSE,

Micron is not an acceptable term for micrometer (millionth of a meter).  There are SI style guides that deal with this (review the sites of BIPM or NPL or NIST):

http://www.bipm.org

http://www.npl.co.uk

http://www.nist.gov

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

sanbas,
First, throw away 2/3 of the units you've listed.  In both inch & metric systems, only use units that vary by a factor of 103:
Inch units
1 inch
10-3 inch, called a 'thousanth of an inch' or a 'mil' (by coatings people).
10-6 inch, called a microinch (μ").
So 0.025 inch is read either 'twentyfive thousanths' [short form], 'twentyfive one-thousanths' [correct but longer] or 'zero point zero two five' inch [decimal form].
If you run into any confusion, use the decimal form.
0.000025 inch or 25 μ" is read 'twentyfive microinch.'

Metric units
103 m = 1 kilometer (km)
1 m = 1 meter (m)
10-3 m = 1 millimeter (mm)
10-6 m = 1 micrometer (μm), still commonly called a micron.
10-9 m = 1 nanometer  (nm)

Second, when writing, never, ever begin a decimal number < 1 with a '.'
Always begin '0.'  So, 0.025" but not .025"

Micron is part of the vernacular of the optics industry in which I work.  Hence "to me", 1/1,000,000 meter = micron.  Internationally recognized standards will still not replace "local" terminology.  My opinion is if one particular way of indicating a measurement works better for communication, use it.  Mistakes are lessened this way.

Regards,

(OP)

This is simple mathematics (no offense meant).  The number 0.1 (inch, mile, whatever) can be read as "zero point one" or "one tenth" or "ten hundredths" or "one hundred thousandths" or ... ad infinitum.

WOW...that little sentence of your just cleared up years of confusion for me!!!

I guess that saying .0001 as "tenth of an inch" is incorrect, thats how i have heard it referred to for years in my shop.  I guess they were just dropping the latter half by not saying "tenth of a thousandths of an inch."

APPRECIATE THE CLARIFICATION, it all makes sense now

I often hear .0001 refered to as "a tenth", but have never heard anyone refer to it as "a tenth of an inch".

My recommendation is to use whatever dimensional nomenclature that clearly communicates the requirements.  If they happen to be "standard" dimensional formats so much the better but the end goal is still communication.

Regards,

I agree with ewh - .0001 is referred to as a 'tenth' because the traditional division of a manual inch micrometer is .001"  Therefore everything is spoke relative to that 'unit' of measure - so 1/10 of that of 'that unit' is .0001", 10 units is .010", 100 units is .100" and so on.

Steve Hebert
Eichenauer, Inc.

I think tgeorge nailed it.  In the US (IMHO) machinists and their peers talk in thousandths of an inch (0.001").  This is because most tolerance information on modern shop equipment is best suited to that scale.  It is oftened shortened to a "thou".
0.01" as 10-thousandths works just fine, just take 10/1000 and there's your fraction.
0.0001" as a 'tenth(of a thousandths)' also works, 1/1000 * 1/10.

To avoid confusion just write out the decimal, use scientific notation if you need to - hopefully whoever is reading your stuff can understand that properly.  If you're speaking and want to be %100 understood just say "oh point oh oh one inches", people will understand even if it's not "elegant"

Funny thought just occured to me, if you wanted to you could say, "1 inch is 25.4 thousandths of a meter" and people would surely look at you funny even though you're correct.

In MY mechanical world, we use "a-hundred thou" or "ten-thou" or "one-inch, one-hundred thou" ......its just the way we talk and think around here.....what's the big deal.
If it's Metric, then we speak Hungarian......lol

In my experience, on an informal basis, it is all thousandths of an inch unless it is microns.  As tolerances get tighter there is more confusion about “ten thousandth”.  This can sound like 0.010” or 0.0001”.  If it is at all important then write it down or at least ask.

Also remember that reading a micrometer is an art.    Lord help you if you are ever part of group standing around arguing about micrometer readings to determine if a part is in spec or not.

tom

Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com

tomwalz said:
"Also remember that reading a micrometer is an art.    Lord help you if you are ever part of group standing around arguing about micrometer readings to determine if a part is in spec or not."

Ahh yes, been there; that is why we went to all digital readouts. Amazing how many users fail to properly zero the devices and keep the jaws clean, especially with micrometers.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
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