Good Measure by Amanda Murphy - Low Shank Every Clamshell Template Set of 2pcs in 1/8" thickness. Allows you to make 1in, 2in, 3in and 4 inch Clamshells. It has markings that clearly indicate the previous row's quilting lines, which no one else has. All with non-slip backing. Can be used with domestic machines.

These rulers are for low shank thickness.

Amanda Murphy Good Measure Quilting Rulers feature a non-skid backing and two colors of lines for ease of quilting.  Directions are included.