Slip-critical connections achieve their strength from the friction between the faying surfaces of the connected parts. They are usually used in connections where dynamic loads occur. The AISC equation (J3-4) gives the slip strength provided by a single bolt in terms of some parameters. These parameters are the mean slip coefficient , the presence of fillers, the minimum bolt pretension force Tb, the number of slip surfaces, and a multiplier that reflects the ratio of the mean installed pretension to the specified minimum bolt pretension. The above mentioned equation does not take into account the bolt spacing and the connection plate thickness, which the Researcher was convinced that they can affect the strength of a slip-critical connection. In this research the effect of bolt spacing and plate thickness was investigated experimentally and analytically using a finite element program. The experimental work consisted of testing 10 specimens by a universal tensile testing machine. Five specimens had the same plate thickness of 10 mm but with bolt spacing ranging between 60 mm to 150 mm and five specimens had the same bolt spacing of 100 mm but with variable plate thickness ranging from 12 mm to 30 mm. Due to the machine capacity only two M20-A325M bolts were used in all tested specimens. The specimens with thickness of 25 mm ,30 mm and bolt spacing of 150 mm were excluded from the research because there test was failed. The effect of bolt spacing and plate thickness was also investigated analytically by using ABAQUS. Three specimens with fixed plate thickness of 10 mm and variable bolt spacing (60, 80, 100 mm) and three specimens with fixed bolt spacing of 100 mm and variable plate thickness (12, 15, 20 mm) were studied analytically. Each specimen consisted of 6 M20-A325M bolts. The finite element model was first validated using the experimental data. The results indicated that the change of the plate thickness had little effect on the slip strength of the connection, and this was reflected by the slight increase of the experimental strength with respect to the theoretical value given by the AISC equation. On the other hand, the bolt spacing had a greater effect and this was noted by the wide decrease of the experimental slip strength with respect to theoretical value of the AISC equation.