Do 1/2" UNF and UNC bolts have a standard threaded section length?

For example how could i work out what length bolt to buy for a required unthreaded shank of say 2" or 3"

Cheers

Yes, there is a standard ratio of length of bolt to length of thread, but for the life ofe me I cannot remember it right now.
However, see the u2u I am just about to send you !
For everyone else, I will post details tomorrow, ( but someone with a better memory may be along any second).

Regards
Jon

Have a look at LAS Aero's website for a good explanation of the various standards (and some very good quality bolts) www.lasaero.com for UNF/UNC the bolts are described by grip length. For American spec bolts it is more complicated.....

Acording to the ansi standard 1.25 is the length of threaded section for all 1/2" bolts under 6" long and 1.5" is the threaded length for 1/2" bolts over 6"

that seems to the case for "standard imperial bolts" for the american designed stuff leaving here. there are of course plenty of "specials"

try these guys,
http://www.nssocketscrews.com/