Ed, AJ uses two Viton O rings on an aluminum contra, there are two of the O-rings in the first picture. So far I have AJ's heads on an Irvine .25, MDS .78, MDS 1.48, Maloney 125, OS LA .65 and a Fitzpatrick .61, nothing has gotten past the O-rings. Now that I have 3 MDS 2.18's I think one of them is next. The one exception is the MDS 1.48 which has one O-ring but also has a perfect seal. By the way, I have a Tartan 1.34 Cu. In. single coming tomorrow and Mr. Davis is sending a head for it in a couple of days.