Radium 6AN ORB to 8.5mm Barb These anodized billet aluminum adapter fittings can be used in any application using a 9/16″-18 O-ring port. This is the same thread pitch used in -6AN (ORB=O-Ring Boss). They all feature FKM (Viton) O-rings for all oil and fuel types. These anodized billet aluminum adapter fittings can be used in any application using a 9/16″-18 O-ring port. This is the same thread pitch used in -6AN (ORB=O-Ring Boss). They all feature FKM (Viton) O-rings for all oil and fuel types.