Aluminum tube cut down the side to create a vibrating chamber. Hole under thumb controlls wah-wah effect by lifing and replacing thumb. Comes in two sizes WW1BK, 10.5"(27cm) long and WW2BK 12.5" (32cm) and both tubes can be purchased as a set WW12BK. The WW1BK has a higher pitch, while WW2BK has a lower pitch, both tubes played together sound great. There is a very good demonstration on YouTube.