A structural device (11) is part of a seat frame (2) and comprises: - a main flange (7) comprising a lower part (12) fitted with a first hole (10), - a reinforcing flange (8) fitted with a second hole (11) and secured to said lower part (12), and - a spacer (9) comprising a first end (13) passing through the first hole (10) and fitted with a first internal thread, presenting a first diameter and designed to cooperate with a threaded stem of a first screw (16) adapted to the anchoring of an anchor piece (6) of a safety belt, and a second end (14) fitted with a second internal thread, presenting a second diameter greater than the first diameter and designed to cooperate with a threaded stem of a second screw (17) adapted to the anchoring of at least one loop strand (51) of a safety belt.
