These after-market sash springs may work in a pinch, but they should only be used after exhausting all other options. They work by creating tension between the sash and jamb, not by counterbalancing the sash with weight, the way it was originally designed. Consequently, the operation of your window will be a rough, friction fit, not a smooth, floating mechanism. If you have a broken sash cord, consider going the extra mile and repairing it rather than installing these. Even you have a spiral balance or spring balance, consider replacing it before installing these. If your weight chamber has been filled with foam or is otherwise inaccessible, these items may be your only option.