By means of crank 1, slider 3 moves along guides 4 of the frame and clamps strip 5. The length of connecting rod 2, connected by turning pairs A and B to crank 1 and slider 3, can be varied by turning head 6 which is rigidly secured to screw 7. Screw 7 has right-hand thread on one side of head 6 and left-hand thread on the other side.
$1640$SC,GC$