A bar clamp apparatus having a pair of opposing clamp jaws, with one of the clamp jaws slidably joined to a handle member. The handle member and attached clamp jaw are slidably mounted on a bar. The clamp jaw attached to the handle member includes a pin which slidably engages a pair of corresponding slots or tracks in the handle member, to allow the clamp jaw to slidably move relative to the handle member. A knob has an attached threaded screw which passes through a threaded bore in the handle member with the end of the screw contacting the clamp jaw on the handle member. Rotation of the knob advances the screw and moves and applies pressure to the clamp jaw attached to the handle member. A workpiece is positioned between the clamp jaws, and the first clamp jaw is moved towards the second clamp jaw by rotating the knob to advance the screw thereby holding the workpiece between the clamp jaws.