The article is dedicated to the problem of broken rubber cord coupling bolts, determined on the basis of the statistics of traction gear failures for the period from 2015 to 2019 based on the results of the AS “Pasažieru vilciens” railway company unplanned repair reports. Due to the large number of unscheduled repairs and the large general downtime of electric motor carriage associated with replacing the broken bolts of the rubber-cord coupling, the question arises of the quality of the M-24 bolts of the rubber-cord coupling of the traction gear. As an object under investigation, we used a broken M-24 bolt for attaching a rubber-cord coupling, taken after unplanned repairs from an ER2 8029-02 EMU motor carriage. The article tested the hardness of the samples, and also determined the chemical composition of the steel. The data obtained were compared with the specification data for steel X-45 according to the requirements of GOST-4543-71. Based on the results of the research, the causes of the failure of the M-24 bolt of the fastening of the rubber-cord coupling of the traction gear are analyzed and the discrepancies of the samples to the requirements of GOST-4543-71. The research process consisted of four stages: the first stage, preparing the sample for research; the second stage, determining the hardness of the metal according to the Brinell scale for measuring the sample hardness using the MIC 10 tool. The results were compared with the bolts manufacturer’s specifications; the third stage, determination of the sample steel chemical composition using the PMI Master PRO installation. The data obtained were compared with the new bolts manufacturer’s specifications. The data obtained were compared with the new bolts manufacturer’s specifications according GOST-4345-71; the fourth stage of the study, drawing the main conclusions and conclusions about the steel used for manufacturing of M-24 bolts for fastening the rubber-cord coupling of the EMUs traction gear.