Abstract: A fastener for use in porous granular or other easily penetratable material includes as a first element a guide element in the form of a flat plate having opposite faces and at least one guide slot which is open along the opposite faces of the plate and which has an open end at an edge of the plate, the slot being at least partially curved along its length. The fastener also includes a material-gripping element in the form of a blade which has a width greater than the thickness of the plate and which is insertable into the slot, the blade having opposite sides which are engaged by and guided by opposite edges of the slot along the entire length of the blade when the blade is inserted into the slot. The blade is deformed by the edges of the slot so as to correspond to the shape of the slot.