The design philosophy of slip-critical connections is to utilize the friction force developed through the clamping force exerted by the pretension of the high-strength bolt. Therefore, the slip-critical connections can have resistance in the direction of the bolt shear. This resistance is affected by the bolt clamping force and slip coefficient on the faying surfaces. This research aims to increase the resistance of the slip-critical connections. Increasing the resistance of the slip-critical connections can be achieved by increasing either the clamping force or the slip coefficient. Thermal spray coating technology was used to increase the slip coefficient. Tests were conducted to investigate the effects of coated material (aluminum or aluminum-magnesium) and coating thickness. Compared to the blast-cleaned faying surface, thermal sprayed coating faying surface results in a greater slip coefficient.