A clamp for a male terminal of a power source, consisting of a frustoconical body projecting out of a base surface that is part of the source against which it rests with its greatest diameter, said clamp comprising: - at least one ring-shaped first portion, with an open section of its circumference, said first ring-shaped portion being adapted to be axially fitted to the male terminal along a second axis, said first ring-shaped portion having such a diameter that a predetermined radial clearance exists when it is axially fitted upon said frustoconical body, said first ring-shaped portion also having two jaws (7, 8) which axially project out of its circumference and located at the ends of the open section of the circumference, said jaws (7, 8) being in opposed, spaced apart relationship, - a clamping device (10, 10a) which acts on the jaws and is adapted to cause them to move toward each other to clamp the ring-shaped portion around the frustoconical body of the male terminal with elimination of the radial clearance, - at least one first plate-like element hinged to said first ring-shaped portion of the clamp on the side from which it is insertable upon the frustoconical body of the male terminal, the first plate-like element being constrained to rotate around a first axis that lies in a plane perpendicular to the second axis, characterized in that said plate-like element is made of an electrically non-conductive material and has a through hole with such a diameter that, when the clamp is fitted upon the male terminal, the through hole establishes a radial interference with the frustoconical body of the male terminal at the greatest diameter thereof proximate to said base surface wherefrom it projects. - at least one ring-shaped first portion, with an open section of its circumference, said first ring-shaped portion being adapted to be axially fitted to the male terminal along a second axis, said first ring-shaped portion having such a diameter that a predetermined radial clearance exists when it is axially fitted upon said frustoconical body, said first ring-shaped portion also having two jaws (7, 8) which axially project out of its circumference and located at the ends of the open section of the circumference, said jaws (7, 8) being in opposed, spaced apart relationship, - a clamping device (10, 10a) which acts on the jaws and is adapted to cause them to move toward each other to clamp the ring-shaped portion around the frustoconical body of the male terminal with elimination of the radial clearance, - at least one first plate-like element hinged to said first ring-shaped portion of the clamp on the side from which it is insertable upon the frustoconical body of the male terminal, the first plate-like element being constrained to rotate around a first axis that lies in a plane perpendicular to the second axis, characterized in that said plate-like element is made of an electrically non-conductive material and has a through hole with such a diameter that, when the clamp is fitted upon the male terminal, the through hole establishes a radial interference with the frustoconical body of the male terminal at the greatest diameter thereof proximate to said base surface wherefrom it projects.