The T3S/MT3S are the same tank, only the MT3S has an aluminum sheathing over it aka "Metal" T3S. Have converted all my older T3 tanks to T3S just by changing to the T3S base and head, mainly due to the fact rebuilding Kanger coil heads, it is easier to rebuild the modular coil head to the full assembly of an older T3. T3S heads can be used in the T3/MT3/Mini T3 (if you get the T3S bases), Evods, Protank/Mini Protank, Protank 2/Mini Protank 2. However, Protank and Evod heads can not fit in a T3S/MT3S tank. The T3S at the bottom flange of the head is a little bit narrower, my a couple micro-meters or such.