JimBinMI, All the "lawnmowers" and finish mowers I'm familiar with have a solid blade, or blades, with a hole in the middle that attaches to the spindle, i.e., one blade with two sharpened ends. However, every brush hog (rotary cutter, shredder, or whatever name they use) that I've seen actually have two separate blades; outer ends sharpened for cutting and inner ends bolted to a plate (disk, pan, stump jumper or whatever name they use for that) which is, in turn, mounted onto the spindle. That allows the blades to swing instead of being one solid blade all the way across. They are much thicker and heavier than lawnmower blades, generally not sharpened as sharp as a lawnmower blade, and they can swing back when they hit something solid and go on around instead of stalling the tractor or shearing a pin. Of course, the extra weight and swinging design allow them to take advantage of the centrifugal force to keep turning. Each blade on my 4' Bush Hog weighed approximately 5.5 lbs. when new. I know some folks who sharpen theirs without removing them from the pan, but I always remove mine and then make sure they still each weigh the same after sharpening.
Bird