Armstrong International A21958-1 Gasket F/B4/B5/A3/A4/A5 F&T

The Armstrong International A21958-1 is a silicone gasket specifically designed for Armstrong boiler models F&T B4, B5, A3, A4, and A5. Made from high-temperature silicone (up to 204°C or 400°F), this 0.5mm thick gasket creates a watertight seal between flanges in your boiler system. This seal prevents leaks and ensures efficient operation by stopping water loss and maintaining proper system pressure. The thin design allows for a compact fit while providing a reliable barrier.