A foot is a glass structure welded to the bottom of a pipe to stabilize the piece between uses. While every pipe has a bottom, not every pipe has a foot. For instance, the GRAV® beaker water pipes have a flattened base, but no additional glass that would qualify as a foot. Some pipes have a single foot, usually in the form of a thick glass disc that's been flared out using a paddle tool. Other, smaller pipes have two feet, usually in the form of small glass marbles welded to the base of the pipe. This style of feet has the added function of preventing the pipe from rolling on a flat surface.