Patchwork Ruler Corner. The ruler is used to sew stitched corners precisely. Single block size 1.5 ", 2.5", 3.5 ", 4.5", 5.5 ", 6.5" inch. Suitable for combination with ruler Half Square. The ruler includes a video tutorial and manual. A ruler was also used in the video Streaks a Clipper. You can find the rulers used in the Related section at the bottom of the page.