Am taking apart my immersion chiller and am making a counter flow chiller. So I went to my local hardware superstore, the lowest one. I have a 1/2 pipe for the base. See the pictures. So most of the chillers I have seen are 3/8". I hope it works well. I basically am following the instructions from the wiki but with a 1/2" female npt end so I can put the stainless steal cam lock on it. Yay pumps.
My parts list (2x)
1/2" coupler with stop
1/2" - 5/8" flush stop (had to do a slight hollowing at one end as it tapers slightly 1/8" or so)
1/2" female adapter
1/2" - 8" piece of pipe (from immersion chiller)
5/8" - 50' rubber hose
I'll post Picts as I soon as I finish the pieces.