CM Designs-Add An Eight Ruler. The Add-An-Eighth combines the speed of rotary cutting quilt pieces with the accuracy of using templates. Once your templates are made, the Add-An-Eighth, with its specially designed lip, will automatically add the customary .125 inch seam allowance to any straight angle and provide a straight edge for your rotary cutter. This package contains one 6x1 inch ruler. Made in USA.