1.1 This classification covers refractory products consisting predominantly of mullite (3Al₂O₃·2SiO₂) crystals that are formed by either converting any of the sillimanite group of minerals, or synthesizing from appropriate materials in a melt or sinter process.

1.2 The 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.

1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.