The 
Duravit 0050500000
 is a plastic fixation plug (or rawlplug/wellnut) used for installing Duravit toilet seats. They are sold as an original replacement part, typically in pairs, to provide a secure and stable fitting into the toilet pan. 
Key Details
Product Type: Toilet seat spare part/fixing plug.
Material: Made of durable plastic.
Use: Designed for top-fixing toilet seats to the toilet pan, creating a stable fit that prevents unintended movement.
Compatibility: Compatible with several Duravit ranges, including the Starck 2 and Starck 3 series, as well as Caro, Happy D, Medici, and Metro models.
Quantity: Typically sold as a pair (two pieces).
Installation Tip: Some sources suggest soaking them in warm water (around 60°C) for 10 minutes to ease installation into the hinge holes.