Certainteed Single hung window ballast flat spring replacement

Your pivot shoe appears to be an older version of our 15-192. This should work for you, but please note that you may need to shave down those bumps you see on the front facing side. This newer Certainteed design doesn't work too well in older windows as-is. Just something to keep in mind.

As for the spring, if you only have one per side then you have the short-tongue Series 170. The long-tongue Series 171 is only used when you need a second spring to go on top of the first.