Window will not stay up also hard to open

Thanks for posting. Some older balances were made in 1/2" increments, but we have found rounding up to the next inch is the best way to go. So if your balance is 5/8" in diameter and 28.5" long, then see the S600-29 Spiral Balance for Tilt-Windows. It looks like you'll need a Red Tip option, which is for a window sash in the weight range of 7 through 29 lbs. Let us know if you have any questions.