The MFILTER Filter, interior air (K 9121C) is a professional-grade replacement component engineered for long service life and reliable operation across all conditions your vehicle encounters. The part is built to the following specification: Length [mm]: 248 mm, Width [mm]: 198 mm, Height [mm]: 40 mm, Filter type: Carbon, Filter type: Zinc. Each dimension is checked against the OEM reference to ensure the component seats and functions correctly first time. Verified to fit ALPINA, BMW models. All compatibility data is cross-checked against the TecDoc database — select your vehicle to confirm the part matches your specific engine and year. This part supersedes original equipment references: 1428102600, 1428102609, 1 987 435 503, 20 93 7114 and 39 more. Matching these numbers confirms a like-for-like replacement with no loss of function. MFILTER is a recognised supplier of automotive filtration components to independent workshops and dealer networks across Europe. All parts are sourced from authorised distribution channels and carry full manufacturer traceability — you receive exactly the same component supplied to professional garages and dealer workshops. If fitment or specifications do not match your vehicle, our technical team can help identify the correct alternative — use the vehicle selector or contact us with your VIN for a guaranteed-fit recommendation. Replacing worn components on schedule preserves your vehicle's safety, reliability, and resale value — and aftermarket parts from established brands deliver OEM-equivalent performance at a fraction of the dealer price. Every part is dispatched with tracked delivery and a 14-day money-back guarantee with hassle-free returns.