Crank 1 and pinion 2 rotate about axis A of link 5. Gear rack 3 slides along fixed guides b-b. When crank 1, rigidly attached to pinion 2, is turned clockwise, rack 3 is advanced to the right and its element a clamps workpiece 4. This stops further motion of rack 3 and the effort applied to crank 1 shifts link 5 to the left, compressing spring 6. Due to its wedge shape, link 5 jams rack 3, locking it in the clamped position. When crank 1 is turned counterclockwise, link 5 is shifted to the right, rack 3 to the left and workpiece 4 is released.
$2398$SG,GC$