The bolt through the center was used to provide additional support to the lamination. Perhaps not needed, but the bolt is the only fastener that extends through the entire lamination. There are a total of 12 screws, each of which is 2 1/2" long and fasten respective trios of the layers. No glue was used because I had none in the shop that would stand up to water. Nevertheless, I think the screws and bolt are sufficient.
I also plan to make jack blocks and jack pads from pressure treated lumber as well.
I saw the rubber chocks on line, and they look fine. I believe that my DIY chocks are a bit taller that the rubber ones I saw on line. Also, they cost $0 and were fun to build.