Sew Square 3™ is a 3" x 3" clear acrylic ruler with easy to use and read black lines and marks. Sew Square 3 includes reference square-up dots for the Wonder Curve Ruler. Sew Square 3™ perfectly squares-up specific blocks in the following patterns: Noel Floral Felicity Happy Together Plant Life Sew Square™ rulers can easily be marked with a permanent marker (ie: Sharpie) for other patterns and other square up points. Marks can easily be removed with a rubbing alcohol or nail polish remover.