So, I just bought a used corksport rad off another member here and it didn't come with the drain plug on the very bottom. I was wondering if anybody knew the thread size so I can get a plug for it. Thank you.

 

I found that the "air bleed" on the elbow is the same as the drainplug on an S4 stock rad setup.
So I'd try that out if you have one handy.
Sorry I don't have the thread pitch or anything.

 

I tried that just a little bit ago, it seals but it doesn't seem like it's the correct thread. It's finally starting to warm up here so I may just throw it in with that and run just some water and see if it holds.