Tool spindle for automatic machines including: - a body provided with a longitudinal axis of rotation (A-A); - a plurality of jaws, constrained to said body, movable between a position of maximum closure, proximal to the longitudinal axis of rotation (A-A), and a position of maximum opening, distal from the longitudinal axis of rotation (A-A); - means (4, 5, 6) for driving the displacement of said jaws between the position of maximum closure and position of maximum opening, and/ or vice versa, and - means (61, 6', 6") for adjusting the travel extent of said driving means, wherein said adjusting means can be activated to modify the position of maximum opening of the jaws, synchronously and symmetrically for all the jaws, independently from the position of maximum closure of the jaws, wherein said body is provided with a through hole coaxial with said longitudinal axis of rotation (A-A), and said driving means include: - a shaft coupling with an actuator of an outer automatic machine; - an operating shaft, alternately shiftable into said through hole in response to a bias given by the coupling shaft, and - a plurality of elements for transmitting the movement of the operating shaft to said jaws, and wherein said adjusting means (61, 6', 6") are arranged on, or associated with, the coupling shaft, and wherein the operating shaft and the coupling shaft are shiftingly and integrally coupled and said adjusting means (61, 6', 6") can be activated to adjust the travel extent transmitted by the coupling shaft to the operating shaft in the longitudinal direction (A-A), characterized in that said coupling shaft includes at least a first portion, integrally coupled to said operating shaft, and at least a second portion (6"), able to be removably coupled to a corresponding actuator of an outer automatic machine, wherein the first portion and the second portion (6") are screwed to each other in the longitudinal direction (A-A) and the extension of the coupling shaft is directly proportional to the screwing degree of the first portion with respect to the second portion (6"), and in that the end of the first portion of the coupling shaft is accessible through the operating shaft for the engagement with an outer adjusting key adapted to be inserted into said through hole, between the jaws, to screw or unscrew the first portion of the coupling shaft relatively to the second portion (6") of the coupling shaft and adjust the extension of the coupling shaft and correspondingly the position of maximum opening of the jaws. - a body provided with a longitudinal axis of rotation (A-A); - a plurality of jaws, constrained to said body, movable between a position of maximum closure, proximal to the longitudinal axis of rotation (A-A), and a position of maximum opening, distal from the longitudinal axis of rotation (A-A); - means (4, 5, 6) for driving the displacement of said jaws between the position of maximum closure and position of maximum opening, and/ or vice versa, and - means (61, 6', 6") for adjusting the travel extent of said driving means, wherein said adjusting means can be activated to modify the position of maximum opening of the jaws, synchronously and symmetrically for all the jaws, independently from the position of maximum closure of the jaws, wherein said body is provided with a through hole coaxial with said longitudinal axis of rotation (A-A), and said driving means include: - a shaft coupling with an actuator of an outer automatic machine; - an operating shaft, alternately shiftable into said through hole in response to a bias given by the coupling shaft, and - a plurality of elements for transmitting the movement of the operating shaft to said jaws, and wherein said adjusting means (61, 6', 6") are arranged on, or associated with, the coupling shaft, and wherein the operating shaft and the coupling shaft are shiftingly and integrally coupled and said adjusting means (61, 6', 6") can be activated to adjust the travel extent transmitted by the coupling shaft to the operating shaft in the longitudinal direction (A-A), characterized in that said coupling shaft includes at least a first portion, integrally coupled to said operating shaft, and at least a second portion (6"), able to be removably coupled to a corresponding actuator of an outer automatic machine, wherein the first portion and the second portion (6") are screwed to each other in the longitudinal direction (A-A) and the extension of the coupling shaft is directly proportional to the screwing degree of the first portion with respect to the second portion (6"), and in that the end of the first portion of the coupling shaft is accessible through the operating shaft for the engagement with an outer adjusting key adapted to be inserted into said through hole, between the jaws, to screw or unscrew the first portion of the coupling shaft relatively to the second portion (6") of the coupling shaft and adjust the extension of the coupling shaft and correspondingly the position of maximum opening of the jaws.