Hi, Ray,
Here is a link to a chart which gives suggestions on blade sizes and their recommended uses.
I am sure there are better charts available but, this is the first one I found and it lists
CAN USE, RECOMMENDED, and CAN'T USE categories for the material and thickness to be cut.
http://ep.yimg.com/ty/cdn/yhst-16765698503918/ScrollChart.pdf
Good luck and God Bless! Spirithorse