Abstract: A snap fastener having male and female parts. The female part comprises two ringlike elements placed on the top and bottom of a flexible lamina. One of these elements has lungs which penetrate the lamina and are guided by a cylindrical part of the opposed element and are folded to the exterior by a conical-shaped part. The upper element is formed by two united pieces, and contains in its interior a movable push-button for opening the fastener. The lower element is composed of two united portions which form a cylindrical-shaped receptacle with upper and lower openings disposed to contain a locking piece having a reversible arched portion movable between opposed stable positions. When the male part is introduced through the lower opening, it contacts the locking piece and exerts pressure thereon so that the direction of the arched portion changes, this movement being transmitted to fingers which move into a groove which encircles the male part.