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 3/4 inch (20mm). The 6030 Flexi-Felt™ model is made of transparent and very durable plastic. The 6030 model is made in North America with our light color wool blend felt. It’s an environmentally friendly alternative to tennis balls and other synthetic products. Once the unit is installed properly it’s 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.