Plastic Insert Plugs the open end of 2" Square Steel Tube 3/16" wall thickness | eBay
Square Tube End Caps - Richmond Wheel & Castor Co
316 Stainless Steel Cap for Square Tube 1-9/16" | Indital USA
3207-1A: End Cap | Wagner Companies
Amazon.com: 1/2" Square TUBING END Cap Plug - Quantity of 8 : Industrial & Scientific
Amazon.com: 1 inch Square Tube Unistrut end caps, Suitable for Frame Hole Tube Plugs, Chair Leg Inserts, Glide Protection for Furniture and Floor by Prescott Plastics – Pack of 4 : Industrial & Scientific
Square Tube Caps - King Architectural Metals
Tubing Caps 3" Square Black Plastic end caps for square tubing 3x3 8-1 – JSP Manufacturing