Having a basic understanding of double hung windows will help when learning how to replace a sash cord. There are two sashes on a double hung window, the upper and lower. The framework that holds the glass in place is the sash. The two sashes slide up and down in the window frame. The jambs are the sides of the frame. Sash weights are heavy oblong shaped pieces of metal that connect to a rope-and-pulley system. They sit in a cavity behind the jambs. The windows are easy to open due to the counterbalance the weights provide.