Inches for an Italian

[ancorato]

It's a simple question, but I think I cannot succeed without the help of a real UK Engineer... (I'm Italian, I hope you understand...)
I need help about the use of the fractional inches: we develop our products in solidworks in mm (accessories for power tools), but we need data for catalog in fractional inches, and we have some problems to find the correct sizes as: if 1mm=1/32, then 1.2mm=1/32" or 3/64"?
Does there is a rule about "rounding up or down"?
I cannot find documentation about it, neither online, neither in my books.
It is possible to use fraction of /128 and /256 or do you use only decimal inches less than 1/64?
Hoping in a quick answer, I say thanks,
Giuseppe.

 

[mappel]

The commonly used method is: 1" = 25.4mm

So 1mm = .03937" (not 1/32")
1/32" = 0.79375mm

 

[ancorato]

Thank you for your answer...
But I still have this problem: for the end-user catalog we need fractional inches, not decimal, and we're not looking for the same precision that we need for production.
Ciao, Giuseppe.

 

[tygerdawg]

Maybe something like this would help?

http://icrank.com/cgi-bin/pageman/pageout.cgi?path=/drillsizechart.htm&t=2

This links lists standard drill size designations (letter sizes), standard fractional inch sizes, and their decimal equivalents.

As you can see, decimal sizes are not always compatible with fractional sizes.

TygerDawg
Blue Technik LLC
Advanced Robotics & Automation Engineering

http://www.bluetechnik.com

 

[Gstoner]

I think what you're looking for is the 'about/approximately' list

(~ / approximately)

yes, 1/32" = ~1mm

The easiest way to do this is by looking up Imperial size hardware (screw, bolts, etc.) There really isn't a 'rule' for rounding up OR down in this case. More of a "what's the closest".

ie: 3/8 screw (.375" diameter x 16 threads per inch) is very close to an M10 screw. Precision-wise, 3/8"=9.525mm, but there is no M9.5 (or a .3937" screw) in standard sizes.

Size-wise, we usually don't go below 1/32" (not down to 1/64" or 1/128"). If it's under 1/32" increments, it's usually in decimal inch.

Most of the time, when us Americans are trying to convert from Imperial to Metric (or vice-versa), it has to do with hardware or metal thicknesses (11ga = .1197" = ~3mm) Hopefully we'll someday actually start THINKING in Metric, so that this little conversion problem we all have will disappear. But probably not too soon

 

[dvd]

If you are providing a product that needs to be installed by tradesmen in the construction industry you should round all of your dimensions to 1/16". Standard "tape measures" are incremented in 1/16" intervals. If you are providing more precision parts then just provide the decimal equivalent in inches and thousandths of an inch.