The invention concerns a fastener comprising a head and a foot comprising a rigid core and three curved flexible wings each joining said rigid core along one side, having opposite a face of said core an inside surface bordered by a longitudinal edge and by a transverse edge, and having an outside surface respectively tapering towards a pointed end which is an opposite end to said head and towards said transverse edge, on respective opposite sides of an inflection plane, each said wing being configured to bend by elastic deformation towards said core; said core comprising a hub and three small walls extending radially from said hub, whereby said core is star-shaped in cross-section; and said inside surface of each said wing is bordered by a said respective small wall which is remotely opposite said longitudinal edge.