Scotty,
I am very impressed with my brand new WOODS HB-72. It is a medium duty BB by WOODS and all plates are 3/8" thick. The mfg suggested to use 40 to 80 hp tractor. But according to the rule of thumb for this 6 ft BB, even wity 6 hp per foot, it require only 36 hp tractor.
I agree with Bob and am going to borrow Bob's earlier comment regarding WOODS BB...."Here is a big heavy duty WOODS blade. This is a beast. The steel is noticably heavier than the other brands. It has an interesting locking system to adjust the scarifier teeth in place. It was sturdy, and could be adjusted without tools, but I would have preferred a simple pin lock. I would say this is the best made blade in this group...."
The HB-72 looks exactly the same as the pics posted by Bob except the HB-72 has six scarifiers instead of five in the pic. I find no problem with the system holding down the scarifiers, in fact it is simpler to operate than pins. All you have to do is hold onto the handle pull it up and the scarifiers are free to move. It's an extremely solid design. Each holder holds down two scarifiers. There are two blades, one front and one back. The back one is a floating gate with horizontal hinge above the blade which can lift open backwards while the BB is towed forward and it remain solid while back fill.
I just started to use the HB-72 and pleased with the unit. In next few months I will use it to clean up about five acres of land with various terrain and slope. I am in the process to develop a outdoor horse riding grass areana (or a riding meadow). The area was full of overgrown twenty years old brushes and blackberry. There are rootballs and cutoff brushes all over the place. I am sure that I will find out the limit of my HB-72.