Steel Tube Connectors by Marni bemark, - Corner Joint 3 way Tube Connector (Galvanized) 25mm Tube Connectors are made of 2mm mild steel and is used on 25mm (1 inch) square tubing.
Amazon.com: CONNECTOR RIGHT ANGLE FOR SQUARE TUBE JOINT 2 WAY PIPE PROFILE PLASTIC 20MM 25MM 30MM 20x20 25x25 30x30 (A=20 x L=36 x L1=36 x t=1.5) : Industrial & Scientific