The disposable self-opener consists of a conical tube shoulder (1) with a mouth (2) produced by plastic injection molding, whereby the self-opener can be inserted in a union nut (16) and screwed on the end of the tube (14). Said opener has cut edges (6, 8) on the inner side disposed obliquely in relation to the direction of screwing. A retaining basket (10) is disposed in the center of said opener, which receives the metal clip (13) of the sausage-like foil packing to be opened so that said clip does not enter the nozzle (19) thereby preventing it from obstructing the flow of the paste or clogging the nozzle.