The aim of this article is a mechanism description aimed at measuring the friction coefficient in the threads of screw joint and consecutive experimental measurement. The coefficient of friction in the threads of a bolt and nut depends on a number of factors, in particular the roughness of the surfaces, the properties of the lubricating film and the angle of the side of the thread. The coefficient is a function of the heat treatment, the quality of the surface protection substance, the value of the screw load and the pitch angle of the thread. The key parameters of the measurements were fastening torque which was set using the torque wrench; axial force measured by axial force sensor; and calculated friction coefficient. The friction coefficient was calculated using the equation of the torque balance in the screw. The value of the friction coefficient was examined on the screw joint of size M20 without the plastic lubricants and with the plastic lubricants. Measured values of friction coefficient were close to the values listed in the norm and prove that plastic lubricants can decrease the friction coefficient in the threads of the screw joint.