I like to make a prototype to see if I like the final result before making a whole bunch of something. I also come up with improvements or better ways of doing things during the prototyping. But you can skip this part. To make a prototype, take a rectangular piece of scrap. Ideally, the long side should be twice the small side. Draw a line across the middle to create two squares, then draw the diagonals of each square to find the middle of each square. With a square, transpose the two centers to the sides of the rectangle so that you can use them as reference. Dimensions might be driven by the scraps available... You can finish it off by drilling a hole and driving a screw to see if you like the finished product.