MAGNETI MARELLI brake disc (360406003901) is precision-machined from high-grade grey cast iron for uniform heat dissipation and resistance to thermal cracking under heavy braking. Key dimensional data — Diameter [mm]: 320 mm, Height [mm]: 61 mm, Brake Disc Type: Cast Iron, Brake Disc Thickness [mm]: 20 mm — ensures the rotor geometry meets OEM tolerances for run-out, thickness, and parallelism right out of the box. Compatible with BMW vehicles; the hub-centric bore and bolt-circle pattern match the original specification exactly. Direct replacement for OE references: 0833055, 0 986 479 056, 0986479056, 0986AB6409 and 78 more. MAGNETI MARELLI rotors are checked for surface hardness and dynamic balance before dispatch, keeping braking distances predictable throughout the service life of the disc. Brake discs generally last 50,000–70,000 miles, though this varies with driving habits, terrain, and pad compound — heavy urban driving or towing shortens disc life considerably. Warning signs of worn discs include visible scoring or lip formation on the friction surface, vibration through the steering wheel under braking, and a persistent grinding noise even with new pads fitted. Disc replacement is an intermediate DIY task; you will need a torque wrench, a breaker bar (some hub-to-disc retaining screws seize over time), and a jack with axle stands — budget 1–2 hours per axle. When selecting brake discs, check that the disc type (vented or solid) matches the original, and look for a protective anti-corrosion coating on the hub and non-friction surfaces to prevent rust jacking. Always replace discs in pairs (both sides of the same axle) to maintain even braking balance, and bed in new discs with the manufacturer's recommended gentle-braking procedure for the first 200 miles. Every part is dispatched from our UK warehouse with a 30-day money-back guarantee and free hassle-free returns.