Restore the smooth operation of your single or double hung sliding windows with this 21-inch window sash balance replacement. Designed for sash weights between 17-21 lbs, this balance offers precise fit and reliable support for both DIY enthusiasts and professional installers. Engineered for durability, it's compatible with installations using standard or winged balances and is ideal for both new installs and repairs. For best performance, we recommend replacing both balances at once. Backed by expert guidance and local service, this essential part ensures long-lasting window function and enhanced comfort for your home or business. Ensure you get the right fit by measuring the length of the metal channel and checking the stamped number, either 2040 or 20D