1955-57 Chevy Belair LS Swap Doug Thorley Headers 4:2:1 Long-Tube Tri-Y Headers Silver Ceramic Coated Primary Tube Diameter: 1-3/4" Primary Tube Gauge: 14 Gauge Collector Attachment: 3 Bolt Flange Collector Diameter: 3" Flange Thickness: 3/8" Bolts and/or Studs Included O2 Sensor Bungs Included Gaskets Included Adapters/Reducers Included, 3" to 2.5"