Vinyl Caps are glides / inserts that go into your patio furniture chair legs or tubes. The plastic on the top is designed to snuggly fit into the space provided, shaping itself to ensure a secure installation. The round but stable bottom is used to keep your chair legs off the ground and prevent scratches on your patio or deck while also keeping the frame safe from corrosion from the inside out. They are primarily designed for the use in 5/8" legs. Our round patio chair glides and the round chair leg inserts fit most common patio furniture chair legs. To insure a proper fit, measure the inside diameter of the patio chair leg and compare it to the dimensions of the patio furniture part dimensions shown in our diagrams. You can find more information about how to measure for patio furniture replacement parts in the FAQ section of our website.