Intermediate fastening element, in one piece, comprising a plate which is preferably substantially flat, having a first face or upper face and a second face or lower face, at least one anchoring element, for example in the shape of a fir tree, projecting from the upper face, and hooks arising through moulding from a region covering substantially the whole lower face of the plate, the hooks, the plate and the anchoring elements being in one piece arising through moulding in a same material, in which, for a hook comprising a stem and a head projecting laterally from said stem, one defines in longitudinal section, perpendicularly to the lower face: - the axis of the hook as being the line perpendicular to the lower face and passing via the middle of the base of the hook at the level of the lower face; - the right delimitation line segment between the stem and the head of the hook as being the first line segment parallel to the axis of the hook, starting from the axis and offsetting to the right, which cuts the envelope curve at two points (64, 65) and which extends between these two points; - the maximum height HM of the hook as being the distance measured perpendicularly to the lower face, from the lower face to the highest point of the envelope curve in said section in longitudinal section defining the hook; - the minimum height Hm of the hook as being the distance measured perpendicularly to the lower face, in said section in longitudinal section, from the lower face to the most remote point of the delimitation segment of the envelope curve defining the hook head; and - the fastening height Ho of the hook, as being the distance, measured perpendicularly to the lower face, from the lower face to the highest point of the section of the envelope curve defining the head and which extends from the lowest point delimiting the delimitation segment of the head as far as the most remote point of the head of the delimitation segment in said section in longitudinal section, characterised in that the plate is substantially rigid, that is at least holds its shape itself, and in particular cannot bend owing to the effect of its own weight; and the hooks are realised with a shape and dimension such that the profile (HM-Ho)/(HM-Hm) of at least some of the hooks, preferably of the hooks, is greater than or equal to 0.55, the hooks, after having been formed in a mould and having been removed from the mould, substantially resuming the initial form which they have in the mould, the hooks being sufficiently flexible to allow them to bend during removal from the mould. - the axis of the hook as being the line perpendicular to the lower face and passing via the middle of the base of the hook at the level of the lower face; - the right delimitation line segment between the stem and the head of the hook as being the first line segment parallel to the axis of the hook, starting from the axis and offsetting to the right, which cuts the envelope curve at two points (64, 65) and which extends between these two points; - the maximum height HM of the hook as being the distance measured perpendicularly to the lower face, from the lower face to the highest point of the envelope curve in said section in longitudinal section defining the hook; - the minimum height Hm of the hook as being the distance measured perpendicularly to the lower face, in said section in longitudinal section, from the lower face to the most remote point of the delimitation segment of the envelope curve defining the hook head; and - the fastening height Ho of the hook, as being the distance, measured perpendicularly to the lower face, from the lower face to the highest point of the section of the envelope curve defining the head and which extends from the lowest point delimiting the delimitation segment of the head as far as the most remote point of the head of the delimitation segment in said section in longitudinal section, characterised in that the plate is