'73 Chargers are 4 bow. Midway thru '71 production, they went from 6 to 4 bow. Of the 4, 3 are the same size and 1 is slightly longer and it mounts to the C pillar and has 2 springs. To install, also get some(10) of those small $1.00 squeeze clips to hold the liner to the roof lip. Once you get it where you want and tight, then use those U clips to hold permanently.