I'm planning on putting D-Ring Tie Downs to my bed but I couldn't get a real clear answer on what type of bolts I'm dealing with so I took one out to see for myself. Looks like a D-ring with a hole greater than 5/8" or 15mm will work. Based on the corrosion and dirt, there are plenty of threads to mount anything between the bolt head and the washer. Use a drill press or a power drill and a file to remove the edge that holds the washing in place. took less than 1 minute. I used a Torx Plus TP50 to remove one. Perfect fit.