Tim and I saw this at Quilt Market last May. The package contains 15 grips and retails at $5.99. They are made by 'The Grace Company'.
These non-slip adhesive rings cling to the back of rulers to help you cut more accurately. We tried 3 rings on the back of a 3 1/2" by 24" ruler. It did help reduce slipping on the fabric but really helped with the ruler on the cutting mat. The more I used the ruler the more I noticed the difference. Being frugal, 3 were enough but I could have used more and noticed a bigger difference. The rings are pressure sensitive and can be removed. The ruler and rings may need cleaning if the rings are changes around frequently.