1.1This classification covers fired refractory brick and shapes consisting predominantly of zircon (ZrO₂·SiO₂) and containing, by chemical analysis, not less than 60 % zirconium oxide (ZrO₂) and not less than 30 % silica (SiO₂).

1.2The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.