This 1/2 x 9 inch seam marking tool is long enough to mark the diagonal of a 6-1/2 inch square. Mark through the slotted center with any mechanical pencil and sew 1/4 inch on each side of the tool. Or mark the sewing line by drawing on both outside edges. Our exclusive grip holds the tool in place while marking. The perfect tool when making half-square triangles! Creative Grids products are made in the USA