Flat to 6/12. A = 4". C = 3-1/2" minimum flange dimension. No. 3RV-AF6: Size: 3", B = 6-5/8" No. 4RV-AF6: Size: 4", B = 7-3/4" No. 5RV-AF6: Size: 5", B = 8-7/8" No. 6RV-AF6: Size: 6", B = 10"