Grav Labs 3" Hammer Bubbler - 25mm Glass (10 Pack) The GRAV� Hammer Bubbler is 3" tall and made on 25mm tubing with an etch label. The body of the bubbler is clear while the mouthpiece, downstem, and feet are colored glass. Its cross-cut downstem diffuses smoke through water, and its feet stabilize the bubbler between uses. No accessories are necessary for using this bubbler, and it functions best with approximately 0.5" of water. This pack includes ten bubblers.