Sorry for the slow reply, I thought Fathers Day was to rest! I had fun loading up the Performer though!
As best as I can find is that the flitting on the end of a regulator hose is "3/8" female flared fitting", maybe someone can confirm that? That solves half of the equation, and no pipe dope on that fitting!
The mystery is the NPT side, my receipt says 1/8", but see attached picture, it looks bigger than that, doesn't it? I found this forum that talks about attaching a regulator hose with 3/8" flared fitting to a old Weber gasser manifold, which is what the guy at True Value said of the adapter and why he stocked it. The other forum as you'll see seems to resolve to a 1/8" NPT. Maybe the 1/8" measurement is the ID (interior dimension)? On this fitting you need to use pipe dope that is certified for LP, I can take a picture of the tube I used if needed, but it's pretty common stuff. Forum link:
http://www.bbqsource-forums.com/invboard/index.php?showtopic=8570 I removed the old brass orifice elbow from the old regulator tube, hopefully the attached closeup pictures should get you the rest of the way but I am here to help if you need anymore detail.