This is a set of Reducer Cones for Scott Drake Headers that have the O2 Sensor Provisions (or bungs) for use with an EFI (Electronic Fuel Injection) System on your Engine. These reducer cones are compatible with the ball and socket style collector. These fit on the Scott Drake Shorty Exhaust Headers for the 65 66 67 68 69 70 Mustang that uses the Ball and Socket Style connection at the header collector. Sold as a set.