Longitudinal shear (10) for cutting a metallic ribbon (90) comprising an inferior fixed structure (12), at least a couple of blades holder shafts (14) each of which is in particular provided of at least a circular blade (18), and activating means able to make rotate at least a blades holder shaft (14) in such a way to determine at least a longitudinal cut of the metallic ribbon (90), and preferably comprising a superior structure (13). The shear (10) comprises stiffening means (30) of at least a blades holder shaft of the at least a couple of blades holder shafts (14) which are able to support and to stiffen the at least a blades holder shaft preferably in a substantially symmetric way respect to an vertical symmetry axis (95) of the same in particular in proximity of the at least a circular blade (18).