OK, so I’m really late getting in on this discussion... I guess that’s what happens when you don’t check in but once every couple of weeks.

The short answer (many other factors are involved) is that a welded connection’s strength is determined by weld length times thickness of weld, and a bolted connection’s strength is a factor of bolt diameter. Again, there are many other factors involved but these are the basic factors.

First, how large is the D ring bracket? The length of weld you get around the perimeter of the bracket will determine how strong the connection. Also, if you use large high strength bolts you’ve got to be careful not to concentrate the stress in a small area or you’ll pull the bolt through the frame rail

I’d check with the D ring manufacturer for some “engineered” recommended connection details.

Dan J