ASTM C126-10

1.1 This specification covers structural clay load-bearing facing tile and facing brick and other "solid masonry units" made from clay, shale, fire-clay, or mixtures thereof, with or without the addition of grog or other mixtures, having a finish consisting of a ceramic glaze fused to the body at above 1500°F (655°C) making them inseparable, excluding natural salt-glazed ware. Two grades, based on permissible variation in face dimensions, and two types are covered, as follows:

1.1.1 Grade S (select), for use with comparatively narrow mortar joints.