The Featherweight Accurate Seam Square simplifies seam accuracy.  Achieve a proper seam allowance fast and easy by lowering the tip of the needle through hole of the desired seam width then use the square to align the edge of the Featherweight Accurate Seam Guide (sold separately).  Fasten the seam guide in place and your seam allowance guide is set. Raise machine needle and be ready to sew! 

Seam Square will accommodate a size 90/14 needle and smaller.