aFe MagnumFORCE Spare Parts AIS Coupling Reducer: (3-1/2 x 2.80)ID x 2LaFe MagnumFORCE Spare Parts AIS Coupling Reducer: (3 1 2 x 2. 80)ID x 2L This MAF adaptor allows for the use of the high performance Euro MAF sensor on US domestic market (USDM) E36 M3. Made of 100% polyurethane, this adaptor has a stainless steel sleeve in the adaptor neck for added rigidity. This coupler inlet diameter is 88. 9mm that matches the Euro MAF and reduces down to 71. 1mm to match domestic throttle bodies. Magnum FORCE Cold Air Intake