The invention relates to a closeable opening device (1) made of a spout fitting (2), a cutting element (3), and a screw cap (4), optimized for assembly and use. To this end, the spout fitting (2) and cutting element (3) are produced as semi-finished goods (5). The cutting element (3) comprises an upper edge (33) at the cylindrical part (30), having recesses (36) distributed uniformly around the circumference. The screw cap (4) comprises ring wall segments (46) on the inner underside of the cover surface thereof, designed diametrically opposite the recesses (36). The upper edge (33) and the ring wall segments (46) slide against each other during assembly, until the ring wall segments (46) engage in the recesses (36) in a form-fit manner. A stable form-fit connection thus exists between the two said parts, allowing greater torque to be transmitted without the problems known from the state of the art occurring.