A handy person from Salinas, California says:
April 4, 2013
I've attached pictures of my channel balance ends, which I am unable to identify from your catalog. It is stamped 2640 BSI and is 27 inches long. Is this fairly standard? Also, the only problem I have with my channel balance is that the cord broke. I was able to restring it with #18 surveyor's line that is twisted pair, but that does not appear to be as strong as the multi-weave cord that was in the balance to begin with. Do you sell the cord? I have a fairly sophisticated work shop and can stretch the spring without difficulty so that I can tie a new cord in easily. (I sent a separate submission on a top sash guide.)
Paul from SWISCO responded:
April 5, 2013
Thanks for posting! It looks like you might have something like our S390-27 channel balance. How does that look to you? Do all the dimensions match?
I'm afraid that we don't have the strings. If yours has broken, we recommend replacing the entire balance system.