A bar clamp has a slide bar supporting a movable jaw assembly. The slide bar is supported in a fixed jaw assembly. The fixed jaw assembly includes a drive mechanism for moving the slide bar relative to the fixed jaw assembly. Mechanisms for expanding the capacity of the bar clamp including the use of straps and two slide bars. Specialized jaws are provided where the jaws may be removable from the jaw assemblies. Additional clamping jaws are provided in addition to the movable and fixed jaw assemblies for varying the clamping force applied to a workpiece.