Abstract: Coupling part for use in a system with flowing fluid, with an integral male part (1) to be sealingly mounted and retained upon aksial insertion into an adapted female part on another coupling part, the female part has at least one internal annular groove or a step for locking the male part. The male part (1) has, for engaging with the annular groove or grooves, steps, integral locking tongues (2, 3), respectively. The free ends of the locking tongues are pointing oppositely of the direction of insertion for the male part (1) into female part, and all the locking tongues are projecting slanting outwardly or have hooks projecting outwardly. The male part of the female part may be provided with at least one sealing element.