65mm Square Tube End Cap (ENDCP65MMSQ) - Richmond Wheel & Castor Co
Amazon.com: Prescott Plastics 2.5 Inch Square Plastic Plug Insert, Black End Cap for Metal Tubing, Fence, Glide Insert for Pipe Post, Chairs and Furniture (10 Pack) : Industrial & Scientific
ELESA, Square, 0.12 in Tube Wall Size, Tube End - 29AU84|NDX.Q-1-1/2X0,120- B 3/4-10 - Grainger