stupid question:  What's the difference between mil and mm?

dingebre wrote on Sat, 15 May 2010 14:06

Coming from an education in mechanical engineering and physics, the

terms "mil" and "thou" are completely unambigous and equivalent. That

said, I think in the world of PCB layout, "mil", "thou", and "mm" do get

confusing, especially to one with little or no machining background or

mechancial engineering studies.

I don't have a mechanical engineering background, and to me "mil" is

unambiguous.  That term has been around for a long time.  Remember when

real to real audio tape was rated in mil thickness?

Quote:

Form my experience, "thou" is more arcane and "mil" is more commonly

used.

"Thou" seems to be something mechanical people use.  For PC boards, its

always mil, inch, or millimeter.  Lately more parts are defined in mm.

Although sometimes you see a datasheet insist on all mm and then everything

is cumbersomely a multiple of 2.54mm.  C'mon guys, if your pin pitch is

really .1 inch, don't pretend it's in mm.

--

Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

There seems to be a cultural difference indeed. Sticking to length

measurements only:

I have heard Australians talk about mils, and it took me a while to

discover that they were talking about millimeters. I also heard British

engineers refer to millimeter as "mil".

Both referred to 1/1000 inch as "thou", probably to avoid confusion...

In Norway and Sweden there is also a mil, but that one is equal to 10

kilometers and not very usable in PCB design ;).

In my neck of the woods, "mil" stands (rather unambiguously) for 1/1000

inch, or 0.0254 millimeter. Then again, I grew up with metric units...

Those readers interested in the the precise(?) what, where, why and how

could look (but probably already have looked) here

http://www.answers.com/topic/mil or here

http://dictionary.reference.com/browse/mil

Have fun (and always check your measurements).

--

Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

There seems to be a cultural difference indeed. Sticking to length

measurements only:

I have heard Australians talk about mils, and it took me a while to

discover that they were talking about millimeters. I also heard British

engineers refer to millimeter as "mil".

Both referred to 1/1000 inch as "thou", probably to avoid confusion...

In Norway and Sweden there is also a mil, but that one is equal to 10

kilometers and not very usable in PCB design ;).

In my neck of the woods, "mil" stands (rather unambiguously) for 1/1000

inch, or 0.0254 millimeter. Then again, I grew up with metric units...

Those readers interested in the the precise(?) what, where, why and how

could look (but probably already have looked) here

http://www.answers.com/topic/mil or here

http://dictionary.reference.com/browse/mil

Have fun (and always check your measurements).

--

Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.