A screw fitting for a pipe comprising an end portion having an end edge, the fitting comprising: - a metal threaded coupling end member defining an axis having an inner shaped portion designated to be mutually faced with the end portion of the pipe; - a metal ring nut that can be mutually screwed with said threaded coupling end member; - a metal clamping element that can be fitted on the pipe to remain coaxially interposed between said threaded coupling end member and said ring nut, the latter having a first inner surface susceptible to come into mutual contact with said clamping element upon the mutual screwing of said ring nut and said threaded coupling end member to promote the relative axial translation of the latter and said clamping element; wherein said clamping element comprises a ring having at least one first annular portion ( 12 ') for contact with said first inner surface of said ring nut and at least one pair of gripping clamps extending transversely from said ring, each of said clamps having a first end portion ( 11 ') facing towards the ring and a second opposite end portion ( 11 "); wherein said shaped inner portion of the threaded coupling member comprises, in sequence, at least one first frusto-conical surface, at least one sliding surface, at least one second frusto-conical surface and at least one abutment surface, said at least one first and second frusto-conical surface ( 43, 44) being coaxial and converging towards said axis; wherein the screw fitting is for use with a gas pipe made of metal material, the ring of said clamping element being a rigid ring, the second opposite end portion ( 11 ") of said clamps being radially expanded towards said axis to define a clamping jaw; and further said clamping element and said shaped inner portion being mutually dimensioned so that upon the mutual screwing of said ring nut and said threaded coupling end member, when fitting a pipe: - said at least one first frusto-conical surface comes into mutual contact with said clamps to permanently radially compress said clamping jaws on the pipe, so that the latter form an annular gripping groove on the pipe to mechanically integrally connect the pipe and said clamping element; - following such mechanical connection, said at least one sliding surface comes into mutual contact with said clamps to allow the integrally joined axial sliding of the pipe and said clamping element; and - following such mechanical connection and said integrally joined sliding: - said second frusto-conical surface comes into mutual contact with the end portion of the pipe to radially compress it, so as to define a first pneumatic sealing means; and - said abutment surface of said threaded coupling end member is at mutual contact with the end edge of the pipe to compress it axially, so as to define a second pneumatic sealing means. - a metal threaded coupling end member defining an axis having an inner shaped portion designated to be mutually faced with the end portion of the pipe; - a metal ring nut that can be mutually screwed with said threaded coupling end member; - a metal clamping element that can be fitted on the pipe to remain coaxially interposed between said threaded coupling end member and said ring nut, the latter having a first inner surface susceptible to come into mutual contact with said clamping element upon the mutual screwing of said ring nut and said threaded coupling end member to promote the relative axial translation of the latter and said clamping element; - said at least one first frusto-conical surface comes into mutual contact with said clamps to permanently radially compress said clamping jaws on the pipe, so that the latter form an annular gripping groove on the pipe to mechanically integrally connect the pipe and said clamping element; - following such mechanical connection, said at least one sliding surface comes into mutual contact with said clamps to allow the integrally joined axial sliding of the pipe and said clamping element; and - following such mechanical connection and said integrally joined sliding: - said second frusto-conical surface comes into mutual contact with the end portion of the pipe to radially compress it, so as to define a first pneumatic sealing means; and - said abutment surface of said threaded coupling end member is at mutual contact with the end edge of the pipe to compress it axially, so as to define a second pneumatic sealing means. - said second frusto-conical surface comes into mutual contact with the end portion of the pipe to radially compress it, so as to define a first pneumatic sealing means; and - said abutment surface of said threaded coupling end member is at mutual contact with the end edge of the pipe to compress it axially, so as to define a second pneumatic sealing means.