This 1/2in x15in seam marking tool is long enough to mark the diagonal of a 10in square. Mark through the slotted center with any mechanical pencil and sew 1/4in on each side of the line. Or mark the sewing line by drawing on both outside edges of the tool. It's the perfect tool when making half-square triangle blocks.The tool slides easily over the fabric until pressure is applied. Then, our exclusive grip holds the fabric in place while marking.Total Size: 1/2in x 15in