what thread size is the fuel filter return port?

[GREASE FIRE]

i want to plug the return line that comes out the top of the fuel filter because it just seems like something is wrong with it. when the truck is shut off i can depress the little tire valve thing and no fuel comes out and it seems like the system should be under some pressure - at least that is how my 6.2 is. And that one does not have any return line at the filter and it has never been a problem.
Basically, i think this system has something to do with the fact that my truck takes a good long crank to start - and sometimes it even shakes/rattles a bit while cranking until it starts. I remember one time i ran out of fuel and did not know why it shut down at first (sender did not work, tank was full a few days ago BUT tank had a leak i did not know about) and when i was trying to start it that same shake/rattle thing was going on.
so if i can plug that return port i can figure out if that is the problem or not. Anyone know what size it takes? I konw the tire valve thing takes a strange size (not pipe threads) so i figure the return one does as well. Anyone know?

thanks,
Paul

 

[LCAM-01XA]

1/8 NPT it is, IIRC.

 

[subway]

1/8 NPT it is, IIRC.

yup just did mine a little bit ago. havent noticed any side affects to it. when you do take the fitting out watch there is a spring and rubber part that comes out you might want to keep "just in case".