**

See: http://www.roadstone.ie/resources/pdfs/Bricks.pdf

See website:
http://www2.nen.nl/nen/servlet/dispatcher.Dispatcher?id=BIBL...
"Nederlandse titel Specificaties voor metselstenen - Deel 1: Baksteen

Engelse titel Specification for masonry units - Part 1: Clay masonry units
...
Engelse samenvatting 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. "