If you have metal sled base chairs that are ruining your floors then you should look at this Flexi-Felt model designed specifically to fit tubing of 1/2 inch (12mm). The 6015 Flexi-Felt model is made of transparent and very durable plastic. The 6015 model is made in North America with a wool blend felt. Its an environmentally friendly alternative to tennis balls and other synthetic products. Once the unit is installed properly its very difficult, almost impossible, for children to remove it. Our sled base models offer unsurpassed floor protection with the largest surface contact area on the market. Our patent pending antiroll system is guaranteed to keep the Flexi-Felt® well aligned. Designed for 1/2" tubing (12mm). Transparent, durable plastic. The product is guaranteed for 5 years.