The study attempted to observe the surface characteristics of the flank lock type precision locknut which was assembled in a vertical type and operates under different tightening speed. The speed setting was in according with the specifications of 4rpm, 6rpm and 8rpm conditions to set up this experiment. A type of 2TML lubricant was used. The experiment investigated the surface characteristics of a locknut, including contact surface flatness, contact surface roughness, and thread surface roughness before and after the designed test. According to the contact surface flatness of the locknut obtained from this study, it was found that the surface of the locknut contacting with the bearing resulted into a deterioration of the surface flatness and surface roughness during the tests. Furthermore, the thread surface roughness has been changed at different thread for different tightening speed during the test, especially at threads 1, 2, 7 and 8. The study found that some of variations occurred in the values of Ra, Rz and Rmax at different thread of a locknut. The variation of Rmax is the most among them.
