Duragrader is supposed to be a good implement, BUT the company has problems,:thumbdown: I would stay away from them unless I could personally go to their place of business.
Weight is your friend when grading, you should try to get all grading type blades as heavy as you can. Now you still need to only get what your tractor will pull, and that is typically the width of your tractor up to maybe 18" wider than your tractor for just a rear blade by itself. I have found that box blades and these road grader type blades work best to be either the same width as the tractor or up to 6" total width wider than the tire tracking width. If you tractor tires measure 72" wide, then I would look for a blade between 72" & 78" in width. Now 78" wide implements are not all that common, so you would either get a 72" blade or depending on your circumstances consider an 84" blade.
These road grading blades are not all built the same. There are light duty, (12"sides) medium duty, (18" sides) and heavy duty (24" sides) to be had. Also the total length of the sides can make a big difference on how good the grader blade works, the longer the better.
I usually recommend the Road Boss, which is very good, but very costly,
Road Boss Grader - Road and Landscape Grading, Surfacing and Leveling, and Material Spreading and Reclamation or the GradeMaster which looks to be pretty good also
GradeMaster Grader Blades. There are many more, you just need to check them out before you buy one. These types of grader blades are very very good at maintaining a dirt road.
Good luck you guys
