Hanging window hitch to keep window open

This looks like a coil balance system. Specifically it appears to be an older version of our Series 140 assembly. You'll need to choose the appropriate spring weights for your window. That 6 and 5 stamped onto the old assembly might suggest you need 11 pounds of support on both sides of the sash, which would indicate you need our S140-11. However, to be safe you might want to obtain the exact weight of the window sash. if the sash weighs 22 pounds, then the 11 pound assemblies should work. Let me know if you have any questions.