Window tension springs

Thanks so much for reaching out to us. I'm sorry to say that we don't carry this sliding window spring and I'm not sure if it's still available. It's very old. 

Would it be possible for you to drill or punch another hole at the end of the spring to accommodate the screw at the corner of the sash? That might be your best bet. Due to its age, I don't think this will be an easy part to track down. You may ultimately be forced to make modifications.