PURPOSE: To enhance the safety of connections by forming in the side of each groove a seat part which accommodates each rib through the rotation of a male element at the end of sliding of the rib into the groove, causing the end of each rib to collide against the shoulder of the seat part, and holding the rib on the corresponding seat part.

CONSTITUTION: In a sequence in which a rib 5 enters a side seat part 13, the first inclined part 101 of an end 15 passes through the edge 100 of a groove 10 against the action of a coned disc spring washer at the start of rotation of the first inclined part 101. After the inclined part 101 has completely entered the side seat part 13 and partial rotation of a male element 1 has been effected, the rib 5 is made to completely enter the seat part 13 by the associated action of a coned disc spring and the second inclined part 102 of the end 15. Thereafter, the rib 5 is held on the corresponding seat part 13 by the elastic action of the coned disc spring provided at a female element. When each rib leaves the side seat part 13, a predetermined force that overcomes the action of the coned disc spring washer needs to be applied.