Previous comment said these washers were made of steel (using a magnet); Well, the existing expander ring on my cork was also made of steel. I bought the car as a CPO with 9,000 miles on the odometer and the figure washer was replaced either from the factory or by a VW dealer; this. Oil change at the dealer when buying the car. So don't worry too much about whether it's steel or aluminum. 1 of 5 used and tightened on this oil change. No immediate problems were observed. Now award 4 instead of 1