Depends
Screws with "all thread" typical of wheelpants and access panels are not load carrying, so after the first thread is through, the rest is just extra . if it is in a load carrying application with a "shanked" screw, the 1-3 threads is a good rule to use..any more than 3, the screw will be "shanked out" and not tightened. The nutplate is a crushed type that makes it self locking, so if the screw does not protrude to at least flush, the self locking is not fully effective. BTW 330Jock,I am also a Piedmont/Usair guy...maintenance side though. Speedbird rocks!