The standard rocker panel for the Base Firebird and Formula was the spear shaped chrome piece shown at the top right. Trans Am rocker panels were plain and never had chrome trim. This rocker trim had a single part number (481546) since it could be used on the right or left side of the car.
Esprit came standard with a wider chrome rocker cover that butted flushly against the standard chrome wheel lip moldings. This trim was wider than the standard and carried separate part numbers for right and left (481539 right and 481540 left).
The wider chrome piece was an Esprit only item but it is common to see these on restored Formula's. Do your homework because most times when you see this rocker panel you are looking at an Esprit cloned into a Formula and not an original Formula.