These are the 4 flat-sided rubber gasket when viewing the cross section that seals the canister edge of the cover to the filter unit base. "These are not "O-rings". Two sides of this gasket are taller to offer more "squeeze" to prevent leaking. The older style were square and could be rotated 4 times for extra life. These can be flipped over once for extra life and have better anti-leakage characteristics..
NOTE: If you have the rare style that uses the round O-ring gasket call me. I probably have them but these are the type that seal the INNER SIDE of the canister and not the EDGE of the canister bottom.
