Andersen Window - Perma-Shield Narroline Counter Balancer, #331Andersen Window Perma Shield Narroline Counter Balancer, # 331 Can be used to Replace: 319, 325 Note: Jamb liners may also need to be re ordered. Sash balancers are metal boxes that contain a nylon cord under tension. The balancer number is a code for the tension and the cord length. The proper balancer must be used to maintain either the lower sash or the upper sash in an open position. If you replace one balancer you should replace both balancers.