The fin on a 500 curved as it went to the front of the car. The fin on the 300 was straight. Also, on the 500 the back part of the chrome went to the top of the fin and on the 300 the back part of the chrome went straight back to the tail light area. In 1957 Ford made a Custom, Custom 300, Fairlane and a Fairlane 500. The customs' had the straight fin and the fairlanes' had the curved fin.