I like using the chains for various barbell exercises like bench press, military press and curls. I haven’t determined how to use them with a back exercise.
Yesterday was arm day and I usually do three different types of exercise: biceps, triceps and forearms.  My first exercise was the biceps curl on the Legend rack.  A bar was already there when I walked up to it.  I looked for the two chains and they were where they usually were by the twin bench press stands. 

The bar was one of the Texas ones which are longer and heavier than a normal Olympic bar of 45 lbs.  This bar is around 55 lbs.  I added the two chains to the ends of the bar and preceded to get stance in front of the bar on the Legend rack.  I muscled it off the Legend,  let it drop to my thighs and realized it might be too heavy to curl.   I started the curl – got half way up and had to let it drop.  I failed to get it and realized that was close to 75-80 lbs.  It varies because the chains partially rest on the floor and as I curl it gets heavy as more chain is lifted off the ground.