This European Standard specifies the characteristics and performance requirements for masonry units manufactured from clay for use in masonry construction (e.g. facing and rendered masonry, loadbearing or non-loadbearing masonry structures, including internal linings and partitions, for building and civil engineering). This European Standard is intended to apply to two groups of fired-clay masonry units: LD units (see 3.4 and 5.2) comprising: clay masonry units with a gross dry density of less than or equal to 1000 kg/m3 for use in protected masonry. HD units (see 3.5 and 5.3) comprising: a) all clay masonry units for use in unprotected masonry; b) clay masonry units with a gross dry density of greater than 1000 kg/m3 for use in protected masonry. This European Standard includes those clay masonry units of an overall non-rectangular parallelepiped shape. It defines the performance related to e.g. dimensional tolerances, strength, density measured according to the corresponding test methods contained in separate European Standards. It provides for the evaluation of conformity of the product to this European Standard. The marking requirement for products covered by this European Standard is included. This European Standard does not specify standard sizes for clay masonry units, nor standard work dimensions and angles of specially shaped clay masonry units. This European Standard does not cover requirements for the following: units for paving, flue liners and storey height clay units and clay masonry units with an incorporated thermal insulation material bonded to the faces of the unit susceptible to be exposed to fire. It does, however, include clay units for external chimney masonry.