When ball joint performance matters, the RODRUNNER BJ-B-1004 delivers — built to the same dimensional and material standards as the original part it replaces. The part is built to the following specification: Fitting Position: Front Axle, Fitting Position: U, Length [mm]: 138, Cast Iron mm, Width [mm]: 65, Ceramic mm, Height [mm]: 65 mm. Each dimension is checked against the OEM reference to ensure the component seats and functions correctly first time. 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: 21687, 29947AP, 31106852536, 37-26623-5 and 10 more. Matching these numbers confirms a like-for-like replacement with no loss of function. RODRUNNER is a recognised supplier of automotive replacement 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.