A barrel, cask, or tun is a hollow cylindrical container, traditionally made of wooden staves bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. For example, in the UK a barrel of beer refers to a quantity of 36 imperial gallons (160 L; 43 US gal). Wine was shipped in barrels of 119 litres (31 US gal; 26 imp gal). A small barrel is called a keg.