Note that in my photo above - showing one of our friend's homemade wooden step-block leveler built just like ours - that it consists of three steps screwed together made by cutting up one long piece of 2X8 redwood board. Driving up onto the highest step provides 6 1/2 inches of lift. One more small piece of 2X8 under the high end provides another 1 1/2 inches, for a total of 7 1/2 inches of lift.
We camp all over the west in campgrounds and boondocking in forests and deserts using up to five sets of these homemade wooden step-blocks. Five sets of homemade step-blocks takes care of us in the worst case situation of three-point leveling - lifting 4 rear duals and 1 front wheel.
We gave up on plastic leveling blocks long ago because we broke them all the time when camping here in the West. A couple of other great uses of these homemade solid wood leveling blocks is they can also be used under our hydraulic jack in soft ground in case of a flat tire and they can also be used under the rear dual drive wheels in case we should ever begin to get stuck in soft ground.
The plastic leveling blocks are compact, light, and work well under the common situations of flat earth, smooth gravel, or paved surfaces in designated campgrounds. Get out of these type of ideal conditions, and for us the plastic blocks would crack and/or splinter.