The ISO nuts of styles 1 and 2 specified in ISO 898-2 and ISO 898-6 are designed to prevent the thread stripping failure mode based on the calculation method called the Alexander's theory. However, it have been pointed out that the thread stripping sometimes occurs in over-loaded bolt/nut assemblies of certain sizes and property classes due to the inadequate specifications in the relevant International Standards. This paper treats the design concepts on ISO nuts for the revision of the above ISO Standards, which is now taking place. The simulation program has been reproduced based on the Alexander's theory, and the calculated values were compared with the specified ones. The results clearly show that there are both over-designed specifications and insufficiently designed ones with higher risk of stripping. Therefore, the possible ways to exclude such problems have been considered based on the distribution of the bolt/nut thread strength ratio calculated. Finally, it is shown that that the most practical way is to change the hardness range of nut, and the program to obtain the adequate specifications is proposed with verification.
2007 by The Japan Society of Mechanical Engineers