ASTM classifies brick used in exposed applications by its appearance.For Facing Brick (ASTM C216) and Hollow Brick (ASTM C652)there are three classificationsin which the last ietter of the series indicated the texture and dimensional tolerances.
TYPE FBS OR HBS. Brick for general use in
masonry This classification is the
default in the ASTM standards for brick.
TYPE FBX OR HBX. Brick for general use in
masonry- where a higher degree or precision and lower permissible variation in
size than permitted for Type FBS is required.These are the tightest requirements.
TYPE FBA OR HBA. Brick for general use in
masonry selected to produce characteristic
architectural effects resulting from
nonuniformity in size and texture of the
individual units.