GRAV® Medium Gravitron® v2This is the smaller version of the Gravitron, but it still packs the same kind of punch you'd expect from a gravity bong. This new and improved version 2. 0 Gravitron boasts a fivefold increase in glass thickness and upgraded platinum cured silicone grommet for a tighter seal. The 14 mm female ground joint now fits any 14 mm male bowl and the flange at the top of the neck makes lifting the bottle a breeze. The Gravitron creates big, efficient hits