The nozzle and air jet size determines the air requirements. The air jet fits inside the power gun and controls the amount of air leading to the nozzle. Nozzles and air jets can be changed, depending on your air compressor. If you have a 3 HP compressor (7 cfm), your best choice is probably the small nozzle. If you have a 5 HP compressor (10-15 cfm), use a medium nozzle. For a 10 HP or larger compressor, use a large size nozzle. Remember, nozzles and air jets must be changed in sets (small with small, etc.) and are available in steel, ceramic and carbide. Nozzles and Air Jets are always in stock at www.tptools.com