For Nissan Sentra Performance 4-1 Design Stainless Steel Exhaust Header Kit (Polished Chrome) Precision machined steel flanges that provide a tight seal at the head and allows a high flow rate through the primary tubes Made From High Quality T304 Stainless Steel For Strength & Durability Constructed With TIG Welded CNC Machine Flange For Percision & Fitment All Tubing Is Mandrel-Bent Comes With O2 Sensor Bung Insertion & Metal Gasket