Item (21, 51) comprising at least two sets (1, 31) of elements (3, 5, 7, 33, 35, 35', 37, 37') assembled to each other, each set (1, 31) comprising a first (3, 33), a second (5, 35') and a third (7, 37, 37') element with the first element (3, 33) and the second element (5, 35') disposed on either side of the third element (7, 37, 37'), the first (3, 33) and the second (5, 35') elements each including a first (2, 4) and a second (27, 28) blind recess and the third element (7, 37, 37') comprising a first and a second through hole, the first through hole of the third element (7, 37, 37') being placed opposite the first blind recess (2, 4) of the first (3, 33) and second (5, 35') elements of each set (1, 31), the second through hole of the third element (7, 37, 37') of one set (1, 31) being placed opposite the second blind recess (27, 28) of the first (3, 33) and second (5, 35) elements of another set (1, 31), each set (1, 31) includes a permanent securing device including: - a first pin mounted in the first through hole of the third element (7, 37 37') and in the first blind recess (2, 4) of the first (3, 33) and second (5, 35') elements, the first pin including, at one end mounted in the first blind recess of the first element (3, 33), first locking means, - a first socket disposed in the first blind recess of the second element (5, 35'), the external wall of the first socket comprising second locking means in said first blind recess and the internal wall being welded to the other end of the first pin or said other end being press-fitted into said first socket, the item (21, 51) being characterized in that it includes another permanent securing device connecting said at least two sets (1, 31), said other permanent securing device comprising: - a second pin mounted in the second through hole of the third element (7, 37 37') and in the second blind recess (27, 28) of the first (3, 33) and second (5, 35') elements, the second pin including, at one end mounted in the second blind recess of the first element (3, 33), third locking means, - a second socket disposed in the second blind recess of the second element (5, 35'), the external wall of the second socket comprising fourth locking means in said second blind recess and the internal wall being welded to the other end of the second pin or said other end being press-fitted into said second socket. - a first pin mounted in the first through hole of the third element (7, 37 37') and in the first blind recess (2, 4) of the first (3, 33) and second (5, 35') elements, the first pin including, at one end mounted in the first blind recess of the first element (3, 33), first locking means, - a first socket disposed in the first blind recess of the second element (5, 35'), the external wall of the first socket comprising second locking means in said first blind recess and the internal wall being welded to the other end of the first pin or said other end being press-fitted into said first socket, - a second pin mounted in the second through hole of the third element (7, 37 37') and in the second blind recess (27, 28) of the first (3, 33) and second (5, 35') elements, the second pin including, at one end mounted in the second blind recess of the first element (3, 33), third locking means, - a second socket disposed in the second blind recess of the second element (5, 35'), the external wall of the second socket comprising fourth locking means in said second blind recess and the internal wall being welded to the other end of the second pin or said other end being press-fitted into said second socket.