cantrelm writes:

Richard, in your article you make a point of saying "I used Grade 5
bolts since ungraded hardware is not suitable for load-bearing
applications. " You do realize that the bumper you are attaching to is
only 3/32" thick and is not rated for load bearing applications.......
This is somewhat of a contradiction don't you think?

The bumper is suitable for load-bearing, for a suitable load.

One problem I understand with ungraded bolts sized about 1/2 inch or
smaller is that hand-tightening torque can stress the shaft close to the
working limit, leaving not enough strength for the applied load. This is
not an issue for the bumper itself.