There are some applications where going to 6 MM is just too big to fit.
I keep a tap and die for 12-24 SAE and some 12-24 SAE Allen screws about 2 inches long.
I can screw them in the die and cut them whatever length and fix the threads when I back the screw out.
With some LocTite it will give you enough bite to hold in many applications and go where 6 MM can't.