This part of ISO 6743 establishes the detailed classification of lubricants for use in family D, air compressors, gas compressors and refrigeration compressors. The intention of this part of ISO 6743 is to provide a rationalized range of the most commonly used internationally available lubricants for air, gas and refrigeration compressors, without resorting to unnecessary restriction by specifications or products description. The primary intention of this classification is to describe and promote the use of the type of lubricant which is best suited for the particular application, specifically with stationary air compressors, with the aim of reducing as far as possible the risks of fire and explosion. Relevant safety rules are given in ISO 5388. ISO 5388 as published in 1991 should be revised to reflect the change from light, medium and heavy duty cycles to normal and severe duty cycles as described in this edition of ISO 6743-3. This part of ISO 6743 should be read in conjunction with ISO 6743-991).