Left stationary acrylic/ Perspex jaw with a standard M4 x 0,7 mm screw, right moving jaw internally threaded with M6 x 0,75 (on 2 bolt guides with springs against backlash). When turning the internally threaded M4 x 0,7 brass screw CW (to the left, onto the M4) the right jaw actually moves to the right with 0,05 mm/ turn - snugging the jaw against the guides' boltheads. 16 turns total moves the jaw 0,8 mm accurately and absolutely repeatable.