This set of two rulers makes an easy and classic allover pattern.  It can produce 1”, 2”, 3”, and 4” clamshells respectively.  The great thing about these rulers is that, when you move from one row of clamshells to the next, the lines on the ruler will line up right on top of your previous row of stitching for perfect placement with no marking!

These rulers are longarm thickness.

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