This leaflet contains the general conditions for tread brakes with composite brake blocks. It describes the required properties of the composite brake blocks, their coefficients of friction and geometry requirements, and furthermore the mechanical, physical and chemical features for both organic and sintered composite brake blocks. It describes the procedure for the issuing of a UIC label for composite brake blocks, and the related test programmes and acceptance criteria to be complied with. This UIC procedure is intended to usefully apply the expertise of UIC experts in assessing braking components via the award of a UIC label. In order to avoid duplication of work, this certificate may then be used by accredited or notified bodies to underpin their own work. The procedure for issuing a UIC label only involves the assessment of safety aspects for the suitable use of the brake blocks and specifies their scope of application (for example 1Bg, 1Bgu, 2 Bg, 2 Bgu, wheel diameter, etc.). The service tests that must be carried out only provide limited information about the LCC for each particular type of use. UIC labels are not issued for specific use of a brake block on a particular vehicle ( UIC Leaflet 541-00 ). The procedure for issuing a UIC label is described in UIC Leaflet 541-00 . Brake blocks and test benches which comply with the provisions of this leaflet are listed on the UIC website. Definitions, test methods and measurements to be performed complete the leaflet.