Drums of many kinds are the most common type of percussion instrument in Nigeria. They are traditionally made from a single piece of wood or spherical calabashes, but have more recently been made from oil drums. The hourglass drum is the most common shape, although there are also double-headed barrel drums, single-headed drums and conical drums. Frame drums are also found in Nigeria, but may be an importation from Brazil. An unusual percussion instrument is the udu, a kind of vessel drum.