I installed them to hold down my tool box.
Here is a little more detailed writeup of what I did.
The box I used is manufactured by Contico, it's called the Tuff Bin. I added two D-rings to each side of the box to attach the box to the truck.
I have extra D-rings installed under the bed-bolts in the front and middle of the bed, a padlock was passed through the D-ring in the corners of the box and the front of the bed, this is all that was needed to hold the box to the bed.
With the box loaded and sitting on the bed mat it does not move. When I went trailing I attached two tie-downs to the other D-ring mounted on the box and attached these to the extra D-rings mounted under the bed-bolts in the middle of the bed.
I have no use for a box in my truck all of the time. When I go trailing or camping this works perfect. It holds my tools, floor jack and a small compressor. On vacation I also had all my carwash stuff in there along with all the tie-downs and bed-net I used to secure my load. Takes about two minutes to put the box in or take it out.