The self-locking nuts that are used in high-speed railway-vehicle bogies and car-body connections are key components of the fastening system. These bogies and connection systems should withstand the high vibrations and shocks that are generated by high-speed operations. Since the first high-speed railway was developed, the antiloose nuts that are globally used in all of the high-speed rail-vehicle bogies and car-body connection systems are single-use limited to prevent nutloosening accidents during train operations. In this study, we developed a double reusable nut for the self-locking nuts of high-speed rail vehicles with a 100-% lifetime improvement. The proposed nut design was subjected to the KS R 9144 and NAS 3350 vibration-performance evaluation tests, and following the DIN 65151 method, a Junker test was performed for an impact-performance test. As the final step, a practical-application test was performed to assess the reusability of the proposed nut for which the self-locking nut of the HEMU-430X high-speed rail vehicle was utilized, and two reusability tests were subsequently carried out to evaluate the safety