1.1 This specification covers the requirements for magnesium oxide (MgO) and aluminum oxide (Al2O3) powders and crushable insulators used to manufacture metal-sheathed platinum resistance thermometers (PRTs), noble metal thermocou This specification covers the requirements for magnesium oxide (MgO) and aluminum oxide (Al2O3) powders and crushable insulators used to manufacture metal-sheathed platinum resistance thermometers (PRTs), noble metal thermocouples, base metal thermocou