T4 to 3″ exhaust inlet flange. Choose between 3″ 16 gauge tube which is 3″ OD and 2.875″ ID or 3″ Schedule 40 pipe which is 3.5″ OD and 3″ ID.Tubing is measured by nominal od whereas pipe is measured by nominal id. Flange is 3D profiled, CNC machined in-house to maximize air flow. Weldable mild steel. Be sure to check the “Stud and Nut Kit” checkbox if you want to add four M10 studs and nuts to mount the turbo with.