Reeds, made either from traditional material or from plastic or metal, are used to produce a musical sound from their vibration by means of an air column. The clarinet uses a single reed, fastened to a hollow mouthpiece, while the oboe and bassoon use a double reed, one side vibrating against the other. The reed-pipes of the organ are generally made of metal, with a thin vibrating tongue to produce the sound. Similar laminae are used in the mouth-organ and harmonica. Some instruments, like the bagpipes or the crumhorn, use covered double reeds, set inside an air chamber.