Abstract: A pieces hold-unit for machine tools such as workstations, transfer machines and milling machines is provided which comprises two parallel supports (12, 13) placed on a plane with at least a first of said support guided, controlled and movable with respect to the other one in order to approach and move them away, at least a first clamp-holder shaft (14) rotary mounted on the said first support and controlled for rotating, a second clamp-holder shaft (15) mounted on the other of said supports. Each shaft holds a clamp opposite to that of the other shaft, and one gear-reduction unit (16) is located at least on board of the support carrying said first shaft to follow the movements of said support and cause the gradual rotation of said first shaft.