I am not sure about the 6-1/2" cut on diagonal. But the 4-1/2" - cut in half from corner to corner. Fold one in half so 2 of the points meet, press the fold with your finger. If you cut on this line, you are cutting on the diagonal. This will give you two (2) triangles. Don't stretch the cut line because this is on the bias and will stretch. So handle with care. On the 6-1/2"
ones, I think they are meant to be cut in half on the diagonal too. Otherwise, these would be cut on the bias, meaning that one of the points would be the top. If any of the instructions have an arrow on, it means to be cut on the grain line. One grain line goes across the width of fabric (or where the fabric has been cut at the store. The other grainline is from top to bottom of the fabric or along the finished edge of the fabric. The finished edge is called the selvage and this is always cut off because it will shrink the most after washing and will pull or distort in a quilt and really messes you up. Check to see about the 6-1/2" before you cut. Hope I explained this to you so you understand. Good luck!