Screw clamp with a head having a reverse-acting and renewable gripping surface

Claim 1

IN A SCREW CLAMP OF THE TYPE USED FOR LIFTING STEEL PLATES INCLUDING A BODY HAVING SPACED OPPOSED PROJECTING JAWS DEFINING A U-SHAPED STRUCTURE AND PIVOTING A PLATERECEIVING SPACE BETWEEN THE JAWS OPEN AT THE PROJECTING ENDS OF THE JAWS, SAID SPACE BEING ADAPTED FOR RECEIVING A STEEL PLATE TO BE GRIPPED BY THE CLAMP AND LIFTED, A SCREW THREADED THROUGH ONE OF SAID JAWS TOWARD THE OTHER JAW, AND A GRIPPING PAD CARRIED BY SAID OTHER JAW AND HAVING A GRIPPING SURFACE FACING SAID SCREW ACROSS SAID SPACE, THE IMPROVEMENT INCLUDING A GRIPPING HEAD HAVING A SERRATED CONVEX PLAT-GRIPPING SURFACE AND BEING PIVOTALLY MOUNTED BY A BALL AND SOCKET JOINT ON THE INNER END OF SAID SCREW WITH ITS CONVEX GRIPPING SURFACE FACING TOWARD THE GRIPING SURFACE OF THE PAD, THE GRIPPING HEAD BEING SYMMETRICAL ABOUT ITS CENTER SO THAT ITS GRIPPING FUNCTIONS ARE EFFECTIVE EQUALLY WELL BY A MOTION OF THE PLATE INWARDLY OR OUTWARDLY AND WITH THE FIRST SERRATIONS AT A SUFFICIENTLY LOW ANGLE AS MEASURED THROUGH THE CENTER OF THE BALL TO THE SURFACE OF THE PLATE SO THAT A SLIPPING OF THE PLATE WILL CAUSE ROTATION OF THE HEAD OFF CENTER AND A GRADUAL INCREASE IN SUCCEEDING TEETH IN THE DISTANCE FROM THE CENTER OF THE BALL TO THEIR CONTACT POINT TO EFFECT FURTHER ROTATION OF THE HEAD WITH FURTHER PENETRATION OF TEETH UNTIL THE DESIRED POINT IS REACHED WHERE ROTATION OF THE HEAD IS STOPPED BY RAPIDLY INCREASE DISTANCES OF THE CONTACT POINTS OF THE TEETH TO THE CENTER OF THE BALL AT WHICH POINT JAMMING OF THE GRIPPING HEAD WITH POSITIVE GRIPPING OF THE PLATE TAKES PLACE.