Movable jaw with bench-screw and guide bars installed

 

I used 5/16 inch round bar stock for my guide bars. You may also make the guide bars from wood. Simply make two battens 3/8 inch by 3/4 inches wide and about as long as your bench screw. Screw these to the bottom edge of the moving jaw, one on each end of the jaw. The battens will run under and rub up againt the lower edge of the fixed jaw. With metal or wooden guide bars the movable jaw when loosened twists and fall either to the left or right, pivoting on the shaft of the screw. The guide bars negate this tendency and keep the two jaws of the vise aligned.