After about 15 batches I started thinking about all grain. I had a 5 gallon cooler with a plastic spigot, which I used for mini-mashes (malt was in a bag and I never had more than 3 lbs of it). Now I wanted to add a ball valve and a copper manifold, but for some reason the hole was too big - about 1". I looked at some bulkheads, and they all were 1/2". Then I asked for advice at bargainfittings.com, and its owner Wayne suggested to use a 3/4"x1/2" NPT SS bushing. It worked for me with a few minor modifications, so if somebody runs into a similar problem, here is a possible solution. This is how it looks.
I added a washer which I found at HD in the electric section, it is quite thin, called 3/4"x1", and I guess is used for some rigid pipes. The washer went outside. The bushing is a little bit too short, and the lock nut is somewhat too thick - after I tightened it, there was only about 1/16 of thread left. So I had to grind the nut slightly, which allowed me to add a 3/4x1/2 adapter. Tested with water, no leaks. I started cutting slits in the manifold, hopefully will make my first AG brew this coming weekend...