Abstract: A fastener including: a shank designed to be throughly accommodated in use with a clearance in a slot of a body part; a hammer-like head which overhangingly extends from both sides of the shank, perpendicularly to a symmetric axis of the shank, insertable in use through the slot under the edge of the latter and oriented parallel to the slot; and an elastically deformable, suction-cap-shaped flange carried by the shank on the side opposite to the head, distanced from therefrom; a rotation of the shank to arrange the head perpendicularly to the slot makes it cooperate by interference under the edge of the slot with a consequent elastic deformation of the flange; the shank carries two elastically deformable oblique arms, which overhangingly extend from both sides of the shank, in a direction perpendicular to the head and so as to reciprocally move away from each other towards the flange, dimensioned so as to elastically cooperate against the shank when the head is introduced through the slot, and then stretch to