Development and deployment of self-braking and self-tightening nuts providing lack of gaps in connections is an important way of increasing the reliability of rail fastening assemblies in both main and inside railway tracks. We have experimentally assessed the functional qualities of self-tightening nuts developed by Agropromimpeks-2000 LLC. The goal of the paper is to confirm experimentally that the power condition of self-tightening is the existence of preliminary tightening of the nut with a certain effort depending generally on preliminary tightness; the geometrical condition of self-tightening is in creating such a configuration of the nut that the moment on its bearing area after removal of initial tightness exceeds the moment in the threaded connection; the operational condition of self-tightening is the existence of deformations of certain size. We have also evaluated the influence of power consumption of a node on nut self-tightening. The studied nut is recognized as promising for both main and industrial railways.