Self adhesive washi tape. Simply cut and stick on your sewing machine centering the pink line with your needle. Use the white lines for a perfect 1/4" seam. Ideal for sewing half square triangles and flying geese. 3/4" wide x 39" long roll. Seam Guide Tape, Self-Adhesive, 13/16" x 10.9yds (2cm x 10m), by Hemline.