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
Amazon.com: cyclingcolors Square Tube CONNECTORS 20mm 25mm 30mm T L Insert Plastic 20x20 25x25 30x30 Pipe (X (4 Way) (A = 20mm)) : Industrial & Scientific
Everbilt 1-1/2 in. x 36 in. Zinc-Plated Punched Square Tube 803057 - The Home Depot
Narrow Flange For 1" Square Tubing - Trade Diversified
Stainless Steel Square Tube Connectors in Square Pipe Fittings - China Stainless Steel Tube, Stainless Steel Connector | Made-in-China.com
Amazon.com: Prescott Plastics 1" Inch (25.4 mm) Square Plastic Hole Plugs Inserts, Black End Caps for Metal Tubing, Fences, Glide Protection from Chair Legs, Furniture and Floors (Pack of 10) : Industrial