After sewing and re-sewing what seemed like hundreds of pinwheel blocks, I came up with my own method for pinning the intersection of the four half- square triangles together.
When I pin a Pinwheel intersection, I like to use 4 pins. I know that sounds like a lot, and most instructions will tell you to use 3 pins, but I get much more accurate results, the first time, with 4 pins. I would rather take the time to pin properly, than have to take the time later to rip it out and try again.Insert the first pin into the intersection of the four triangles, entering through the backside of the top rectangle. Push the pin through the intersection of the four triangles on the bottom rectangle. Make sure the pin remains level in all directions.
The next pin is the extra one that I like to use to stabilize the vertical movement of the seams Place this one about ¼” below the first pin, but parallel to the upper cut edges of rectangle. Now place 2 pins inside the seam allowance on both sides of the seam and parallel with the seam. These two stabilize the horizontal movement of the seams. Now remove the first pin that was inserted through the intersection. Sew the seam.
This might seem like a lot of effort just to pin a seam together, but if you are particular about points matching, give it a try.