I'm with sassysews2: I do that so often I'm reticent to purchase anything!
For my rulers I have one sheet of very fine grit sand paper that I cut off a 1/4 x 1/2" piece. One dot of Elmer's glue has held these dots for years on the back of my rulers. Couldn't be less expensive nor more useful. Love it. At least this one time I remember WHY I have sandpaper in the sewing room.
