Shop › TO4 Turbo Mount Flange Image 1 of 3 Image 2 of 3 Image 3 of 3 TO4 Turbo Mount Flange from $135.00 TO4 1/2' mild steel or stainless steel turbine inlet merge flange with 2 1/2" or 3" starter tubes. Size: Select Size TO4 / 2 1/2" inlet TO4 / 3" inlet Material: Select Material Mild Steel Stainless Steel Add To Cart Added! TO4 1/2' mild steel or stainless steel turbine inlet merge flange with 2 1/2" or 3" starter tubes.