Abstract: A first tube (1) is axially slitted (2) in order to be elastically compressible. The end portion of the first tube (1) has exterior convexly curved engagement formations (3) on the tube tubs formed by the slit (2). The tube tubs (11) can be elastically compressed in order to be introduced through a fitting mantle opening (8) in a second tube element (7). The opening (8) has a width, which is less than the inner diameter of the second tube element (7), and thereby defines internal engagement formations which cooperate with the external engagement formations (3) on the first tube element (1). The tube elements (1, 7) can simply be connected and detached by elastic compression of the tube tubs (11) and axial displacement of the first tube element (1).