MFILTER Filter, interior air (K 9121) is manufactured to OEM tolerances, ensuring a direct-fit replacement that restores your vehicle to factory specification without any modification. Technical specifications — Length [mm]: 248 mm, Width [mm]: 198 mm, Height [mm]: 40 mm, Filter type: Zinc — are verified against the OEM data sheet to guarantee fitment accuracy and performance parity with the original equipment. Compatible with ALPINA, BMW vehicles; use the vehicle selector above to confirm exact fitment for your make, model, and engine variant. Fitment data is sourced from TecDoc, the authoritative European parts catalogue. This part supersedes original equipment references: 1428102500, 1428102509, 1722, 17534 and 38 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 from our UK warehouse with a 30-day money-back guarantee and free hassle-free returns.