Geberit 52.5mm Flat Gasket for Flush Valve, a specific spare part designed to ensure a watertight seal within compatible Geberit concealed cisterns. 
Key Details and Compatibility
Product Type: A flat, circular replacement gasket or seal.
Dimensions: It has an external diameter of 52.5mm and an internal diameter of 19mm.
Function: The gasket creates a secure seal between the flush valve body and the valve seat basket inside the cistern, preventing water leakage.
Compatibility: This gasket is compatible with the flush valve (part no. 241.290.00.1) used in the following Geberit concealed cistern models:
Geberit Sigma 8cm concealed cisterns (models from 2016 onwards).
Geberit Sigma UP720 concealed cisterns (models from 2010-2016).