Barrel is a large, cylinder-shaped container made of wood or metal. The sides of a wooden barrel are made of staves (strips of wood), bound together by metal or wooden hoops. The staves are wider in the middle than at the ends, which makes a wooden barrel bulge in the middle. This shape increases strength, although it wastes space in shipment. The heads (top and bottom) of the barrel are flat wooden circles that fit into grooves near the ends of the staves. Barrels that hold liquids usually have a bung (hole). Bung also means the cork or plug used to fill the hole. A common use for wooden barrels is to store wine. Metal barrels, or drums, have a number of uses, especially in the storing and shipping of chemicals, paints, oils, and petroleum.
Skilled workers called coopers made barrels by hand for hundreds of years. Now barrel manufacturers use labor-saving machines, and cooperage (cask making) has become a large and important industry.
The barrel is a unit of measure for ale and beer in the United States. A U.S. beer barrel, which is also used for ale, holds 311/2 gallons (119 liters). In addition, the 42-gallon (159-liter) barrel is used as an international unit of commerce for petroleum.
