I looked up the pattern for the LeMoyne star. If you need the corner square, you need to measure the side of the diamond between the points where the seam line will be. That is the finished size of the square. Then add 1/2 inch to that measurement and cut out one and sew it to one diamond. If it fits, you are set. or enlarge or decrease to fit. If you have 1//4 graph paper, you could lay it on the diamond and mark where it would fit and then make a square from the graph paper. Hope this will help.