Note that the nut and ferrule assembly is made of two pieces, with the ferrule being a compression fitting used to secure the smog tubes to a series of ports on the cylinder head.
Sold individually, 8 total needed for smog installation. Application is 1968 289-2V, 302-2V, and 302-4V all with manual transmissions. Tube dimensions 5/16" O.D. x 1.560" long. C6AZ-9A484-B