An external minisplint device comprises an elongated body (2) which supports at least one pair of clamps (3, 4; 3', 4'; 103, 104) each of which is capable of securing at least one pair of transverse bone bolts (F), longitudinal guide means (5, 5', 105, 106) associated with the elongated body to guide the longitudinal translational movement of at least one of the clamps (4, 4'; 103, 104), at least one longitudinal adjustment screw (6, 6', 107, 108) which can rotate within the elongated body and which engages a corresponding threaded hole (13) formed in the clamp capable of translational motion for selectively positioning it along the longitudinal guide means, the screw having a head (7, 7') which partly projects from the end of the elongated body, means for axially immobilising the adjustment screw when it is rotated. The axial immobilising means comprise at least one smooth key, and preferably a pair of smooth gauged keys (15, 15', 19, 110) inserted in the elongated body in tangential contact with the base of a circular groove (17) formed in the head (7) of the adjustment screw (6).