An air line is a tube, or hose, that carries a compressed air supply, e.g. to inflate tyres or power compressed-air tools. Air line is most commonly used for supplying compressed air to air tools in workshops and in road vehicle air brake or railway air brake systems on larger vehicles or rail cars. The most common sizes of air tubing are one quarter inch and three eights inch outside diameter tubing although a complete range of tubing in both standard and metric sizes is available. Air lines are also used for diving where s compressor or a hand-powered air pump supplies air to a diver.