Doug's Headers D306 1-3/4" 4-Tube Shorty Metallic Ceramic Coated Exhaust Header for Big Block Chevrolet 67-81 Thick flanges (3/8 inch to 5/8 inch) with no warping CNC mandrel bent tubes for an accurate fit and a better flow Precision formed long transition collectors that reduces backpressure Heavy gauge tubing (16 and 14G) for longer life Header tubes are pre-polished for a better appearance