Abstract: A decking extrusion for use in forming the deck members used to construct outdoor decks, docks, and similar structures is disclosed. The extrusion has an elongate planar base panel (7) with a first elongate side edge (8), and a spaced parallel elongate second side edge (9). At least one first elongate leg member (12) extends the length of the first side edge of the base panel, and at least one elongate second leg member (15) spaced from and parallel to the first leg member extends the length of the second side edge of the base panel. A first locking element (17) is formed at the distal end of the first leg member, and a corresponding locking element (30), sized and shaped to receive a second one of the first locking elements therein, is formed at the distal end of the second leg member. The extrusion may also be provided with an intermediate stiffening leg (126) having a transverse flange (127) formed at its distal end parallel to the base panel to add structural rigidity to the extrusion.