Plug valves use cylindrical or conically tapered rotors called plugs. Stopcocks used in laboratory glassware are typically forms of conically tapered plug valves. The fuel elements and channels are vertical but arranged conically. It is conically shaped with a crater in diameter. Its basal part is almost cylindrical, but often conically widened at the base. Round-bottom flasks often have one or more conically tapered ground glass joint openings, or "necks". They are conically shaped metal funnels and often have ridges down the sides.