Allen wrench size for 6.2 exhaust pipe plugs? Help
 

Ran the engine on the hose today (6.2 MPI) leaning over the engine with a mirror. There is what looks like a pipe plug, one at the front and one at the rear (bottom side exhaust manifold) that tighten with what looks like close to a 1/2" allen wrench. The rear one on my exhaust manifold is leaking there. I tried a 1/2" ratchet, too big, 3/8" was too small. Anyone know what size allen wrench those plugs are? Looks like all the plug needs is to be removed and reinstalled with some thread sealer. If anyone has had this happen to them I would appreciate how you solved the issue. I'm hoping for an easy solution this time -:)

Thanks