patent 5353548
Hello there!
It appears your hardware matches our 15-087 pivot shoe and 15-086 housing, which is designed to use the Series 180 coil springs. Compare our dimensions to your old parts to confirm they match up. These parts are also non-handed. We don't recommend using a heavier or stronger spring. We highly advise replacing your springs with ones that have the exact same weight rating. Stronger springs would actually make the window harder to close, not easier to open.
Look for a number stamped on your pivot shoe or coil spring that will tell you what weight you'll need. If there aren't any numbers, you'll need to remove and weigh your window sash. Then, you'll divide the weight by the number of coils on both sides of the window to determine the correct strength option.