Parts:

4 2 hole x 4 hole plates

6 1" x 8" bolts

6 1" nuts

Put the bolts through 2 plates, through the frame tubes, through the other 2 plates, and loosely put on nuts.

The last two holes of the plates should extend past the end of the tubes.

The pictures show a 7th nut welded on. You'll install that later so don't worry about it just yet.