self - opening plastic closures having a pouring spout including a flange , a cutting member that is moveable in the spout and a screw cap for actuating the cutting member . in this invention , the cutting member carries out a translatory cutting motion by the rotational movement of the screw cap . in order to open the sealed packaging , to which the plastic closure is attached , different torques are brought to bear . according to this invention , first means and second means engage with one another successively to produce different advance paths for each revolution of the screw cap .