Very sturdy, solid plastic, good quality gaskets. I chose the pastic set instead of metal since the plastic is the same material as the intake manifold and it will expand at the same rate as it heats and cools down. Fits BMW X3 E83 3.0d 160kW (218HP), April 2006 (NOT FACELIFT). No need to buy the metal caps. Thank you, Tadeusz!