Designed specifically to fit angled furniture legs that do not have a swivel tip, the 6128 Flexi-Felt® model fits round tubing of 1 1/8 inch (28mm) and square tubing of 1 inch (25 mm). Its patented design allows the entire felt to remain on the floor regardless of the chair leg angle, greatly increasing the durability of the felt and preventing the accumulation of dirt under the felt. Like all other Flexi-Felt® products, the 6128 model is made with our wool blend felt. It’s an environmentally friendly alternative to tennis balls and other synthetic products. It has been proven to reduce floor maintenance costs by over 50% as well as reduce furniture movement noise by 90%. See the test results using a sound meter. Once the unit is installed properly it’s very difficult, almost impossible, for children to remove them and the chairs remain stackable.