dwight, the term Heavy Duty was defined, not by me personally, but by a consensus of a few differnet TBN members of which I was one. It was used in the photo comparison thread from a couple weeks ago. But that said, the term is simply our opinion and does not take metal gauge into account, nor does it take metalurgy into account because those things could not be easily shown in photos.
We defined a HD bucket as one that had welded reinforcement on the cutting lip and the bucket sides, PLUS had some sort of square or round tube welded to the top lip of the bucket.
For mounting a center bucket hook (and this is just my opinion) I would not mount a center hook on any top lip that was not somehow reinforced. The reinforcement could be in the form of an OEM supplied HD bucket or in the form of angle iron (as Henro did) or tube welded onto the top lip of the bucket.