While the threads are the same as a paintball tank (US standard for CO2, CGA 320), the threaded portion of the regulator is not deep enough for a paintball tank's pin valve. You need to purchase an adapter. I purchased this one:
Regulator Converter
Also, most typical paintball CO2 tanks will not fit inside the enclosure; they're either too tall or too large. This is the only one I could find that would work, but it's nearly perfect:
JT IVT Co2 Tank - 9 oz
It's ~3/16" too short, but too short is easy to fix. Just put something underneath it!
So far it works great, and in the long-run, I'll save so much over using the 16gram CO2 cartridges which I've found to be a pain in the a** to use anyway.