DNA Motoring HDSNA02L4 Stainless Steel 4-1 Exhaust Header Manifold Replace stock restrictive headers and increase horsepower and torque. Made of High Quality T304 Stainless Steel Material. TIG Welded CNC Machine Flange. Gaskets, bolts and nuts are included. Inlet: 2.00" X 1.25" Rectangular. Outlet: 2.50". O2 Sensor bung is welded on headers so stock O2 sensor can be plugged in. Professional Installation is Highly Recommended (No Instruction is Included) Vehicle Application: 2002 2003 2004 2005 2006 Nissan Altima 4Cyl (Except Hybrid). Does NOT fit Sentra or Altima V6