Abstarct: High-RPM diesel engines have large power to weight ratio, which causes increased cyclic thermal and mechanical tension in the engine, that directly affects bolts function and cause a complicated situation. Estimating the exact amount of clamping force, the relation between torque and pre-loading force, friction coefficient, functional forces, bolts fatigue life during high pre-loading forces are the main issues of specific bolts joints with high strength. In this research, first, the process of high-strength bolt clamping in a high-RPM marine diesel engine with torque-angle clamping method is studied analytically and experimentally. After finding the accuracy of the manufactured bolt in class 12/9 applied torque, ultrasonic lengths changes and also clamping forces in all steps were measured. In order to investigate the effects of different parameters on clamping process, the new and worked manufactured bolts were applied and their functions have been compared. In addition to that, in order to find out the effect of coating, the bolts friction coefficient in 2 situations (with and without phosphate coating) were studied. The results show that in the first step of clamping the new manufactured bolts small plastic deformation in the thread position cause reduction of clamping force. In the next steps, it’s observed that increasing the friction coefficient under the head of bolt can affect clamping force. Also, lack of phosphate-zinc coating, although the thread was greased, can increase the friction coefficient and decrease the clamping force, which can be controlled by the angular clamping method. In the length-changing measuring by the ultrasonic method, it’s observed that changes in the speed of ultrasonic wave have approximately linear changes on clamping stress in the shaft of the bolt. Checking the results of this study show that axial stress has the main effects on ultrasonic wave’s changes, but shear stress can reduce the speed of the wave. In total, the relation between ultrasonic wave’s changes and applied stress in a real clamping process to the plastic area is calculated. By this formula, we can estimate the clamping force with 10% error. Next, by the calculated friction coefficient, the amount of clamping force estimated in real condition then the effect of external forces and heat is studied analytically and experimentally. In order to study on bolts function in the situation of the engine working, fatigue test is done which verified the unlimited life time of bolt in internal combustion engines. In the following, in order to find the effects of the manufacturing process on the fixed bearing bolt the comparative fatigue tests are done. The results illustrate in low clamping force and high fluctuating force, threading after heat treatment have better function than threading before heat treatment. The process of manufacturing of bolts head in similar loading, the durability of cold forge fatigue is better than the hot forge. While by moving forward to the loading condition of clamping and real situation of the engine working, failure is on the thread instead of the head.