The specification of brick begins with identifying its usage. Most brick manufactured and used are facing brick, commonly specified by reference to ASTM C 216 Standard Specification for Facing Brick. Facing brick used in veneer or structural brick masonry walls is widely preferred over other siding materials because of its desirable appearance. As a result, most brick is chosen on the basis of its color and texture: These properties should be specified by indication of a particular manufacturer's color or blend and/or by approval of a brick sample panel that includes the full range of brick colors and textures. Other appearance characteristics covered by ASTM C 216-95a include dimensional tolerances, chippage, warpage, and out of square. The Specification provides three Types of brick classification depending upon the degree of permissible variation of these characteristics. Type FBS covers brick for general use in masonry. Type FBX covers brick for general use in masonry where requirements call for a higher degree of precision and lower permissible variation in size than permitted for Type FBS. Type FBA covers brick for general use in masonry selected to produce characteristic architectural effects resulting from nonuniformity in size and texture of the individual units. When specifying the brick size, the width, height, and length should be specified--in that order. The Grade of brick is used to specify the physical properties required for the purpose of ensuring freeze/thaw durability. Grade SW brick are intended for use "where high and uniform resistance to cyclic freezing is desired and where the brick may be frozen when saturated with water." Grade MW brick may be used "where moderate resistance to cyclic freezing damage is permissible or where the brick may be damp but not saturated with water when freezing occurs." The measurement of the Initial Rate of Absorption (IRA) is specified in ASTM 216, but the value is not. IRA is not a measure of a brick's durability. The property is measured to assist the specifier in selecting a mortar compatible with the brick.