Amazon.com: Prescott Plastics Made in USA 0.875 Inch Square Plastic Plug Insert, Black End Cap for Metal Tubing, Fence, Glide Insert for Pipe Post, Chairs and Furniture (10 Pack) : Industrial & Scientific
2" X 1/4" Structural Fiberglass Square Tube at ePlastics
Pack of 25) 2" Square (14-20 Ga 1.85" - 1.92" ID) Black Plastic Tubing Plug, 2 Square inch End Cap 2"x2" - Steel Fence Post Pipe Tube Cover Insert | - End