The gas welding and brazing process mainly uses oxygen and acetylene mixtures but an oxygen and propane gas mixture can be used. Gas welding and brazing is now commonly used in the air conditioning industry, the roofing industry for lead burning applications, and in forges for heating applications. Gas cutting uses oxygen and propane or acetylene mixtures although the oxygen & propane mixture is the more popular due to costs. It is important that the correct tips and nozzles are used for the fuel gas (aceylene or propane) being used.