Skunk2 308-05-0410 Pro Valve Spring Retainers K20A - K20A2 - K20Z1 - K20Z3 - K24A2 Engines Titainium - 42% Lighter than OEM Steel Retainers - 7? Keeper Seat - Pair with Alpha Series or Pro Series Valve Springs - Must Use Skunk2 P/N 312-05-0010 on 2005+ K Series Engines