When drop hammer a is lifted upward, tripping lever 1 runs against stop d and its end b is raised, there-by opening the tongs and allowing the hammer to drop. As the hammer drops, latch 2 drops between the tong jaws, keeping them spread. When the tongs are lowered to grip shackle e of drop hammer a, latch 2 is lifted by the shackle and spring 3 closes the tong jaws. End b of tripping lever 1 drops down and locks the tongs.
$176$SL,GC$