....add to this...CLASS A...
When you are sitting on the scales and your TRAILER is 10K (or more)...you need Class A. This is true even if your gross weight (again...while sitting on the scales) is less than 26K. The "kicker" in this scenario is the TRAILER weight while sitting on the scales.
That's how it was "simply" explained to me years ago here in NC while I was sitting on the DOT scales.