Please explain US nut/bolt/screw sizes

[FilthyPierre]

As a young feller who grew up with the metric system I don't really understand what 4-40, 8-32, 10-32 sizes for nuts/bolts/screws mean. I take it it has something to do with the thread size and pitch. A lot of my tools are metric and don't quite fit the American kits I have.
Could someone please explain ?
Thanks,
FP

[Aussie_Man]

The most common of the UNF American sizes are the .05" (some pinion sizes), 1/16 (more pinions and much used on XXX), 5/64, 3/32 (very close to 2.5mm motor screw size but too small, probably the most common of these sizes). Hope this can help ya!

[Nairb]

Yes, those are what size allen wrenches fit in american screws, but that's not what he's asking. I've forgotten exactly what those numbers mean, but I think the 40 in "4-40" means there are 40 threads per inch. I'll find out and post it unless somebody beats me to it.

[Aussie_Man]

Oops, that last message is about the Annlen wrench sizes, 4-40 I think is 4/64th's of an inch in diameter and 40 threads per inch. (5-40 would be bigger in diameter. 5/64th's of an inch.) This is my closets guess but I wouldn't be surprised if this was miles out.

[Walter]

The U.S. or standard sizes refer to threads per inch, 1/4-20= 1/4 diameter 20 threads per inch. 8-32= 3/16 diameter with 32 threads per inch. When going below 1/4 inch the diameters are listed as numbers 8- 32 6- 32 5-40-4-40 ect.

[Walter]

Oops, a number 10 = 3/16 dia.

[foo]

Try this link: http://www.efunda.com/designstandards/screws/screws_intro.cfm

It will explain it all..
I was confused too until I found that site..
:-)

[FilthyPierre]

Geez, information overload http://www.rccaraction.com/ubb/smile.gif Thanks, that clears it up - that's a pretty good site for other engineering stuff too. Thanks again.

[pp13b]

thats 1 bad thing living in australia,u just cant go to a bolt bar to get any special bolts,eg:4-40..