Vinyl replacement window parts

Hi, our vinyl replacement windows no longer stay open when raised. They are double hung sash windows with top and bottom tilt. The tip beyond the rod is red and the rod measures 18 inches by 9/16 diameter. Thank you for your help!

Thank you! after I wrote, I found your parts identifier tool and ordered the 600 series balance. It has already arrived and my husband installed it this morning. The window is fixed and we will be ordering parts to repair the remaining windows. Thank you so much! You have saved us thousands of dollars in new replacement windows. I should add that the repair was quick and easy.