11 has a projection 16 directed toward the cylinder 2 with which it rests in the groove 3 a selection jack 17 provided with a convex prominence 18 on both sides in the central portion the interior part of which rests in the bottom of the groove 3 and the exterior part of which rests against a presser cam 19 the upper portion of this jack 17 furthermore determines a planar face 20 by means of which it interacts with an electromagnetic selection system 21 while in the lower portion an interior foot 22 is defined and rests with its end on the bottom of the groove 3 and an exterior foot 23 forming a hairpin shape with it and having a heel 24 by means of which it interacts with opposing cams 25 this assembly of the system comprises a stationary part which in relation to each of the stitch forming systems in the machine includes a cam 5 for actuation of the needles 1 a cam 10 for actuation of the elastic jack 6 a cam 12 for actuation of the intermediate jack 11 two electromagnetic selection systems 21 two cams 25 for actuating the selection jack 17 and the presser cam 19 which maintains.