The Trelleborg Sealing Solutions Type TRK are specially designed radial oil seals reinforced with a metal insert but without a spring energized sealing lip and a wavy rubber covered outer diameter. STEFA CD type are available with flat rubber covered outer diameters. These types are not recommended for use in heavily polluted environments.--The type TRK are specially designed radial oil seals reinforced with a metal insert but without a spring energized sealing lip and a wavy rubber covered outer diameter.