Parking brake for disc brake, comprising: - a calliper having two side walls spaced apart from each other delimiting a space for receiving a portion of a brake disc, said side walls being connected to one another through a connection structure extending astride of the disc space, - means for supporting at least a pad at each one of said side walls, - a electromechanical thrust unit connected to one of said side walls of the calliper and adapted to push the pads against the brake disc to lock it, wherein said electromechanical thrust unit comprises: - a piston adapted to lock the pad against the brake disc, - an electric motor, - a male/female screw assembly (16, 17) connected between the electric motor and the piston for transforming the rotating motion generated by the motor into a translating motion which can be applied to the piston, - hooking means connecting the piston to a female screw of the male/female screw assembly (16, 17) so that they translate together in the direction of a central axis of the piston, wherein the hooking means comprise locking means (58, 59, 61) automatically locking the female screw to the piston when the preassembled male/female screw assembly (16, 17) is pushed in a thrust seat of the piston, characterized in that the locking means (58, 59, 61) comprise an elastically dilatable closed ring received in an annular groove of the piston and suitable for elastically snapping in an axial abutment configuration against a shoulder of the female screw in response to an introduction of the female screw in the thrust seat of the piston, and in that the female screw forms next to the shoulder a wedge-shaped surface at least partially tilted with respect to the central axis so that: - during the introduction of the female screw in the thrust seat of the piston, the wedge-shaped surface radially enlarges the closed elastic ring in the annular groove, allowing a thrust portion of the female screw to be positioned in a predetermined position in contact with the thrust seat of the piston, and - upon reaching the predetermined position of the thrust portion, the wedge-shaped surface releases the closed elastic ring, allowing for an elastic shrinkage thereof in radial direction such as to axially engage the shoulder and prevent the female screw from coming off from the thrust seat. - a calliper having two side walls spaced apart from each other delimiting a space for receiving a portion of a brake disc, said side walls being connected to one another through a connection structure extending astride of the disc space, - means for supporting at least a pad at each one of said side walls, - a electromechanical thrust unit connected to one of said side walls of the calliper and adapted to push the pads against the brake disc to lock it, wherein said electromechanical thrust unit comprises: - a piston adapted to lock the pad against the brake disc, - an electric motor, - a male/female screw assembly (16, 17) connected between the electric motor and the piston for transforming the rotating motion generated by the motor into a translating motion which can be applied to the piston, - hooking means connecting the piston to a female screw of the male/female screw assembly (16, 17) so that they translate together in the direction of a central axis of the piston, - during the introduction of the female screw in the thrust seat of the piston, the wedge-shaped surface radially enlarges the closed elastic ring in the annular groove, allowing a thrust portion of the female screw to be positioned in a predetermined position in contact with the thrust seat of the piston, and - upon reaching the predetermined position of the thrust portion, the wedge-shaped surface releases the closed elastic ring, allowing for an elastic shrinkage thereof in radial direction such as to axially engage the shoulder and prevent the female screw from coming off from the thrust seat.