A clamp (5) comprising: an upper housing (12, 112) and a lower housing (10, 110), coupled together around a hinge pin (50, 133), the upper and lower housings having a pair of jaws (20) on a first side of the hinge pin (50, 133), and handles (11) for compressing gaskets to separate the jaws (20) on a second side of the hinge pin (50, 133)； an elastic loading spring (54) to oppose the joint compression of the handles (11) and to push the jaws (20) together； at least one stop (34) to prevent the jaws (20) from closing completely and to keep the jaws (20) in parallel alignment when no force is applied to the handles (11) to overcome the elastic loading force of the spring ( 54)； and an adjustment mechanism for adjusting the separation of the jaws (20) characterized in that the adjustment mechanism comprises an adjustment screw (38, 138), a washer clip (46, 149) and an insert (22, 122) ； said adjusting screw (38, 138) comprising a screw head (42) and a threaded rod (40, 140), the rod being pushed through a separation hole in the lower housing (10, 110), the adjusting screw (38, 138)) held in place around the lower housing (10, 110) by the washer clip (46, 149), and the insert (22, 122) to fit into a recess in the housing upper (12, 112), said articulation pin (50, 133) being attached to said insert (22, 122)； said insert (22, 122) comprising a central block (24, 124) with a threaded hole (26, 126) therein, radial arms (28, 128) extending from the central block (24, 124) and wings stabilizers, (36, 136) molded integrally with the central block (24, 124) and the radial arms (28, 128), the stabilizing wings (36, 136) being at an angle with respect to the radial arms (28, 128 )； said stabilizing wings (36, 136) being for coupling the upper housing (12, 112) in precise alignment with the lower housing (10, 110)； wherein the threaded hole (26, 126) is intended to accommodate the adjusting screw (38, 138) so that the threaded hole and the adjusting screw allow adjustment of the
