at an angle of not more than 135 u00b0 with respect to the axis of the support column 10 and such that when the trigger rod is fully retracted a line passing through the pivot point c and the pivot point d between the other extremity of the pull rod 20 and the swing leg 22 lies closely adjacent to the pivot point a in which position the gripper jaws will be firmly interengaged this arrangement allows a powerful gripping action throughout the range of operation and at the same time achieves this through a minimum of travel of the trigger assembly a torsion spring 60 is disposed in the bights 36 and 62 of the support column 10 and the control link 18 normally to urge the swing leg 22 to the full open position as is shown in fig3 the control link preferably is constructed of a deep channel member whose legs 66 and 68 are essentially triangularly shaped and which are disposed between the legs 38 and 40 of the support column in close adjacency to the inner sides thereof as shown in fig2 the control link is fastened pivotally between legs 38 and 40 of the support column by a member 70 which in the preferred embodiment comprises a pivot pin which passes through apertures in legs 66 and 68 is suitably widened at the outer edges of the support column legs 38 and 40 and around the central portion of which pin is wrapped the coil of the torsion spring 60 two other pivotal members 72 and 74.