RRP,that is the best. I'm the one with a medium egg and can't obtain a factory extender. I got my ss bolts, nuts and washers in the mail today, and put my extender together.The medium isn't big enough to stack butts on, but I'm hoping for two decker ribs with it. I purchased 3" stove bolts which leaves a little over 2 inches between the grids. Maybe that will help with your calculations, Lost in Utah. Good luck.