NOS K/H disc brake lower ball joints
But as to tell hardness, there is no way for the naked eye, and then the enthusiast, to tell any difference.
EDIT:
Well, i think i have gotten some of this figured out for all of us.
Part numbers most likely have to do with the length of the bolt, and the thread pitch of the bolt and block.
Fine thread and course thread.
And the big full size Chrysler tuna boats, use a 5/8" inch diameter bolt, in the LCA.
Here's a picture of my stash, what i currently have.
You probably can see different pitch of the threads.
But i wouldn't have any idea at all in calling them light duty, medium duty, or heavy duty.
I know there is different length's of the "bolt" throughout the years, and the body styles, so that most likely has got to do with part numbers.
But as to tell hardness, there is no way for the naked eye, and then the enthusiast, to tell any difference.
EDIT:
Well, i think i have gotten some of this figured out for all of us.
Part numbers most likely have to do with the length of the bolt, and the thread pitch of the bolt and block.
Fine thread and course thread.
And the big full size Chrysler tuna boats, use a 5/8" inch diameter bolt, in the LCA.
Here's a picture of my stash, what i currently have.
You probably can see different pitch of the threads.
But i wouldn't have any idea at all in calling them light duty, medium duty, or heavy duty.