Fremco silicone sealing, 42 mm (KA1079-42, Millennium part 516155), seals the duct entry on Fremco cable blowers so jetting air stays in the duct instead of leaking at the machine. Four pieces are required per setup. The molded silicone conforms to 42 mm duct OD and stays flexible in cold weather, holding pressure through long fiber optic cable blows. Wear parts like these directly affect achievable shot length, so crews typically carry spares on the truck. Available from Millennium with Fremco sealing kits, cable gaskets and duct clamp sets.