A multi-range auto-advance bar clamp used for clamping work pieces together which may upon release of the brake instantly and automatically adjust from a wide open position to any desired closed position. The multi-range auto-advance bar clamp may comprise a slide bar, a movable jaw, a sliding jaw, a body, a drive assembly and a brake, an advancement mechanism, a rigid structural body extension and a slide rail. The jaws of the clamp are adjustably separated and positioned about a work piece. A mechanism for controlling the speed with which the clamp automatically closes may also be provided.