This is the rubber seal that is used on all u bolt shackles 1941-1957. The seal fits inside the cup and seals the shackle to keep the grease inside of it. This is a New Old Stock part and once they are gone we will never have them again. 2 Required per Shackle. On CJ models 8 are Required and Pick Up Truck, 4WD Station Wagon, 4WD Sedan Delivery 4 are Required.