Parts to replace old spiral rod?

These old wood window spiral balances aren't made anymore. We usually suggest our Series 500 non tilt spiral balance and 17-012 bottom balance bracket. We've been using this combination to repair this kind of window for decades. 

To install these balances, you would drop them from the top on the side of the sash. Use a screw like our 33-017 to attach the balance tubes at the top. Now raise the sash and have someone hold it up while you attach the 17-012 bottom bracket to the bottom of the bottom of the sash with a screw (33-090). 

With your finger, bring up the spiral to the bracket and use a tool like our 75-005 to turn the spiral clockwise three times, then hook it to the fork of the 17-012. Repeat for the other side and try the sash. If it creeps down, give the balances another turn or two, but no more than that. Winding a balance too much could break it.