This is a sash balance used on both single and double hung wood windows. Used to replace an existing or update an old pulley and weight counter balance for a window 10 lbs. or less. Steel constructed balance include spring retraction and aircraft cable lifters. Will replace Duplex, Fabco, Preset and Superior sash balances. If your windows (sashes), are having problems staying up when opened, it may be that your sash balances or hardware needs to be replaced. The sash balances hold the weight of the window pane, over time, the springs can wear out or fail. Replace your sash balance for a smoother operation of your window and allow fresh air to enter your home with a window that stays open.