[John Rogers]

That is the proportioning valve and it provides a differential pressure front to rear. I bleed mine with it on and I don't know if it can be bench bleed? Check the article on brakes here on the PP site for details. The other part, if it is the flat, about 1/8 inch thick piece of material is a wiper that keeps dirt from going into the seals by wiping the rod of the shock. For a street car I would enlarge the hole with a razor knife and use it. If you are talking about the thick, black thing, that is the bumper and should most definately be used or get some that do fit. Good luck.