Abstract: A device for the connection of two tool portions has in one of the tool portions a cylindrical fitting pin (2) and an annular surface (3). The other tool portion (4) is provided with a mating bore (5) and an annular end face for receiving the fitting pin (2), and it has two diametrically opposed, radially extending internal threads (12) each with a screw (14, 13) provided with a ball (17) or a conical recess (15). In a transverse bore (6) of the fitting pin (2) is arranged a radially displaceable tightening bolt (7) which at one end has a conical recess (8) cooperating with the ball (17) of one screw (14), and at the other end has a ball (9) which cooperates with the recess (15) of the second screw (13). Both balls (9, 17) are rotatably mounted in a ball socket (10, 16) of the tightening bolt (7) or the screw(s) (14), respectively. On tightening one of the screws (13, 14) these act upon the tightening bolt (7) so as to press together the annular surface (3) and the end face (11).