Curl Stop Anti-Curling Rug System (Pack of 4 Corners) Pack of 4 corners. Holds tight to rugs, not your floors. Works over carpet or hard surface floors. Proven to work both indoors and outdoors - Simple to apply Invented by veteran rug industry experts - A secret of interior designers for years A Grade from FakeSpot.com for honest reviews as compared to competitors D Grade. Patent Pending #US20120285613 - 97% Amazon approval - Made in USA by original inventors, not inferior imitators.