HBT user Pickles is selling a heavy-duty bulkhead kit for $12 (he found a bunch of surplus ones- pretty much the same thing McMaster charges $90 for)- I've bought a few, and so have a bunch of other users. Your hole diameter should work just fine.
Never mind HERMS- he was just being thorough in his answer. For what we're talking about, here's the basic process:
You want to attach a ball valve to your 15 gallon kettle/keggle/metal vessel.
-order yourself a bulkhead from Pickles (PM him on HBT). He will include for $12 (plus small...
The bulkhead will attach to the keg, giving you a female 1/2" npt connection on both the inside and outside of keg. To hook to your ball valve, assuming it has female ends, you would just use a 1/2" npt nipple to connect the two. The bulkhead will clamp down tight on the keg- it's pretty slick...
HBT user Pickles is selling these surplus bulkheads. I bought a couple, and they are on par with the high-end fittings McMaster Carr sells. Worked great, w/ no leaks. He is charging $12 each, and has a lot of good feedback on them.
I just sent him a message today to see if he has more left-...
Hey Pickles- how many of these do you have left? I might be interested in a couple more, and I have a buddy who might want a few. I can pick up locally again for all of them.
Thanks!!!