The securing of screw caps is performed in the following manner: During the process of closing a tank with a cap the cap is firstly guided in standard way onto a thread of the tank and only then the safety projecture slides on the top of the thread with blocking cuts. During further rotation of the cap the safety projecture jumps over the cuts in the body of the thread and after the complete screwing the safety projecture is behind the cuts made in the thread of the tank.<IMAGE>
