I don't know if it is a "standard" but 3 exposed threads is what is considered acceptable at several large plants that I am familiar with.
Ralph
As been practiced at our work site minimun of 3 threads exposed out must be complied when tightening flange connection. Whether this a standard, I am not too sure aswell. I believe the manufacturer can advise you on stardard specification.
Thorangle,
In aerospace applications, three threads minimum must be visible outside the nut. The reason for this is that bolts with rolled threads are allowed two pitches of 'incomplete thread'or 'lead thread' (basically run-in of the thread rolling tool). Furthermore, most nuts are designed with a one-pitch chamfer, which gives a total of three threads visible to ensure complete thread engagement. QED
The only standard I have seen for this subject is DIN 78 Bolt End Protrusions. It requires 3 threads protruding beyond the nut if the nut is a self-locking type and 2 threads if the nut is a regular free spinning type.
