"Diagonal Seam Tape by Cluck Cluck Sew is a perfect solution for sewing straight diagonal seams without having to mark any lines! The special washi tape is strong, thin, and removes cleanly after sewing projects. Simply place the tape in front of the feed dogs with the red line in front of the needle as the stitch line. The black lines on either side of the center line represent a perfect 1/4"" seam allowance and are a great resource to use when making half square triangles, or learning to keep a perfect 1/4"". Each roll is 10 yards. "