<p>Prestressed anchor bolts installed using the torque method are subjected to installation torque and post-installation residual torque, both of which significantly influence bolt strength. This study developed a mechanical model to analyze the stress characteristics of bolts. Experiments under four washer cases, 304 steel washer, nylon washer, no washer, and aluminum washer, were conducted to assess bolt stress state, and the model was validated using experimental data. The impact of torque on bolt strength during installation and service was then evaluated. The main findings are as follows: (1) During tightening, bolt torque and axial force increase linearly with applied external torque. Post-tightening, residual torque, balanced by nut–washer friction, correlates linearly with prestress. (2) Reducing thread friction and lead angles increases the torque-to-axial force conversion coefficient and residual torque, whereas lowering nut–washer friction decreases residual torque but enhances conversion coefficient. (3) Nylon and 304 steel washers enhance the torque-to-axial force conversion coefficient and reduce residual torque, whereas aluminum washers reduce the conversion coefficient and increase residual torque. Among the tested cases, nylon washers achieved the lowest residual torque and the highest conversion coefficient, despite lower compressive strength, which may limit certain applications. (4) Bolt strength during installation depends solely on thread helix and friction angles, decreasing as they increase. Post-installation, under equal prestress, residual tensile strength increases with larger thread helix angles but decreases with higher nut–plate friction. These insights are essential for the safe design of prestressed anchor bolts.</p>