1 Pc 5/8" OD 1/2" ID SQUARE CLEAR ACRYLIC PLEXIGLASS LUCITE TUBE 36" INCH LONG | eBay
Amazon.com: Prescott Plastics 1 1/2” (38.1 mm) Square Plastic Plug Insert, Black End Cap for Metal Tubing, Fences, Glide Protection for Chairs and Furniture (4 Pack) : Industrial & Scientific
Square Plastic Tubing Manufacturers Suppliers
10PCS 1" Inch Square Plastic End Cap Tubing Hole Post Plug 1 inch 1x1 Post Tube | eBay
Aluminum Tubing – Square for Nylon Connectors – 1″ x 1″ w/ Single Channel for .218" Material - Eagle Aluminum
Plastic End Caps For Square Tubing Bungs inserts Blanking Plugs Furniture Feet | eBay