Black plastic plug size is 1” x 1”, fits 1" outer diameter square tubing; Flexible ridges allow these plugs to hold firmly in place and also fit most 1” square tubing; measure your tubing size before purchasing. Made of heavy-duty, high-quality plastic. Flexible ridges allow these plugs to hold firmly in place and also fit a variety of square hole sizes. These easy-to-install plugs serve as a long-lasting solution for many household or outdoor projects, including replacements for fence/railing post caps, gate railing post protectors, trailer frames, post pipe stake caps, wrought iron bike racks, wrought iron end plugs, or any square openings. Provides smoother furniture movement; patio chairs glide across the floor, reducing noise; protects your patio surface, patio chair feet, and patio legs from damage.