I can only speak from first hand experience. It can take 18650 and 18350 single or x2. It comes with a different spring cap but I have only used 18650 and 18350. It accommodates both button and flat top 18650's. You have seen mine I'm sure. Awesome top quality mod. I will hang onto mine as it is an awesome top quality product.
Just watched the PBursardo video and he says it takes all 3 sizes... 18490 if I'm not mistaken.
I will have a Zmax on Tuesday! Thanks for the suggestion Markus!