Our patented design cup locks furniture and caster wheels in place without any slipping or sliding on hard surface flooring. The specialized rubber O-ring on the bottom of the caster cup safely grips the floor without any risk of floor damage. The rounded wheel slot is perfect for wheels up to 2" in diameter and 2-1/4" wide, cradling them firmly in place. These also work well on many flat-footed furniture items which makes these great for almost any room in your home…pianos, game room equipment, pool tables, exercise equipment, treadmills and more…These are heavy-duty caster cups that are virtually unseen under most furniture. Set of 4 will easily support up to 2200 lbs. From the Manufacturer This product is protected by a bulletproof 5-year warranty: if it breaks, cracks, or fails to do its function in anyway, just tell us and we’ll send you a free replacement, no questions asked.