IntroductionThis and the other parts of ISO 6336 provide a coherent system of procedures for the calculation of the load capacity of cylindrical involute gears with external or internal teeth. ISO 6336 is designed to facilitate the application of future knowledge and developments, also the exchange of information gained from experience.Design considerations to prevent fractures emanating from stress raisers in the tooth flank, tip chipping and failures of the gear blank through the web or hub will need to be analyzed by general machine design methods.Several methods for the calculation of load capacity, as well as for the calculation of various factors, are permitted (see 4.1.12). The directions in ISO 6336 are thus complex, but also flexible.Included in the formulae are the major factors which are presently known to affect gear tooth pitting and fractures at the root fillet. The formulae are in a form that will permit the addition of new factors to reflect knowledge gained in the future.