The Audi came with metal caps and Nitrogen new. Yes there are green plasic caps, they look like crap on a nice set of wheels. I used the metal cap however every week I loosen the caps and tighten them and a shot of silicone on the cap occassionally. We didn't see any leaking from the stems on my daughters car. She did get a nail which is what they were fixing when the ripped the stem off.