Abstract: A small crown-head bolt and a double floating plate nut seized each other after 4 times of disassembly, and it was found that the bolt had worn seriously after disassembly. In this paper, macro and micro morphology observation, chemical composition analysis, mechanical properties test, metallographic structure observation, and comparative test verification were carried out to analyze the main reason for the bolt wear failure. The results show that if the convergent nut has a smaller closing, the friction force between the bolt and nut threads will increase abnormally, resulting in rapid wear. The material properties of the bolt and nut are similar. Thus adhesion occurred between the bolt and nut during friction match, and then wear occurred.