Wood window sash balance for a 8 lb. window, or 16 lbs. if one is used on both sides. This sash balance style has been used by a variety of manufacturers of windows for a variety of decades. It fits a 3-1/4 in. by 6-3/8 in. pocket that has been mortised about 2 in. above the centerline of the window frame. It features an all steel construction, with a coil spring inside that retracts aircraft cable lifters as it offsets the weight of the window (vent). 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.