The metal part is 24inch long, without including the plastic part on the ends.

It looks like whoever replaced this balance before didn't have the correct bottom balance shoe. They used a top balance fitting, instead.

I believe what you actually need for your Jones window is a custom made 24" long channel balance with a 19-039 top and 15-004 bottom. Does that look good to you? If so, please let me know how many you need and we can get started.