Originally Posted by
retro71
I speak a little North American, shakiba, let me help.
A brushhog, in other regions called a bushhog, is a large tractor sized/strength mower for places that have way too much vegetation for a regular lawn mower to handle. The shear is the blade, the bolt is what keeps it in place, and the grade refers to how much strength it can withstand in certain situations.
I know this is very layman, but hey...it's really not mumbo jumbo, honest! :-)
Humbly added, please correct me if I've translated out of turn!