The Mercedes Back Brake Disc 166 Small Star (Part No. 166 423 00 12) is a rear brake disc designed for various Mercedes-Benz SUVs, particularly those built on the W166 platform, such as the ML-Class and GLE models produced between 2011 and 2019. The "Small Star" refers to its specific size variant within the range of compatible brake discs for these vehicles, typically intended for standard braking systems rather than high-performance or heavy-duty versions. This disc is manufactured to OEM specifications and is often used as a direct replacement part. Made from high-strength cast iron, it generally features a ventilated or solid design, depending on the exact model application, to ensure effective heat management and long-term durability.

Functionally, the rear brake disc plays a crucial role in the vehicle’s overall braking system by assisting with balanced stopping power and vehicle stability. During braking, the rear discs help absorb part of the kinetic energy, especially during sudden or high-speed stops, working in tandem with the front brakes. While front brakes typically handle a larger portion of the braking force, rear discs like the 166 423 00 12 contribute to even wear distribution, reduced stopping distances, and improved handling under load. This disc is particularly suited for standard driving conditions and offers dependable performance and safety for everyday use in Mercedes-Benz W166 series vehicles.