I'm going to take a wild and arbitrary guess that the individual chains wouldn't see more than a max of about 1000lbs force of tension...
What kind of chain do you have, welded or non welded? Most likely its welded. On the chain somewhere there should be some identification markings, they will be raised letters. There should be a number of some sort... 3, 4, 7, 8, 10... or some variations of that. Like it could be a 3 or it could be a 30 or a 300... but those will all mean the same thing.
Now, any chain that fits the application your using it for is going to fall into one a few categories... it doesn't really matter which one.
The shittiest chain you could possibly have is 1/8" grade 30 which is good for about 400 lbs of directly loaded force on an undamaged chain.
What size chain is it(thickness)?
Grade 70 carbon steel chain is one of the most common for use in transportation, load hold downs etc. Things like boomers would use this kind of chain. 1/4" chain of this type is good for around 3200 lbs in an undamaged and directly loaded situation.
And these weight ratings are working load ratings. Meaning you could run these chains all day long at those load ratings. They probably wouldn't snap until extremely higher numbers... like 15000 lbs. But good thing to keep it mind is that any momentum will build up force very quickly. They say the average 200lb guy that falls 6' can exert over 6000lbs of force on a tie off point. So if your using the chains for tugging, you'll want the heaviest duty you can get
Haha There are other products that work much better for those applications though.
So, if I were to answer your question directly. I would say use grade 70 chain of the largest diameter that will still fit into your torsion bar unit. If your buying new stuff, the grade and manufactuer symbol should be on the links in raised letters... probably atleast one every 10 links I would guess. Should have a 7, 70 or 700 on it.
As a QA guy, I would probably want to make sure your getting quality material... as in, the symbol and grade is there and the symbol is legit and from a reputable company. Also, there would probably be material specs with the "lot" of chain. Like a mill test report for the metal used and other documentation.
