The clamping force in a bolted joint is the load that acts on the joint elements to keep them together and resist any external loads they may experience. These loads are usually vibrations and/or tensions and can be static or dynamic.
When assembling a bolted joint, we convert rotation into displacement. The applied torque rotates the screw, which, due to the helix of its thread, advances axially in the joint until the screw head is seated. From that moment on, the applied torque generates tension in the axial direction (preload). This tension is transmitted to the parts, clamping them.