1.1 This classification system covers the classification of rubber-grade carbon blacks by the use of a four-character nomenclature system. The first character gives some indication of the influence of the carbon black on the rate of cure of a typical rubber compound containing the black. The second character gives information on the average surface area of the carbon black. The last two characters are assigned arbitrarily. 1.2 All rubber-grade carbon blacks for which a number is currently assigned at the time of publication of this classification system are listed in Table 1 together with some of their typical properties. ASTM classification numbers (“N” or “S” designation) not listed in Table 1 have either been withdrawn or are not currently assigned. The use of inactive or unassigned N or S designations is prohibited until such a time as the designation is officially reactivated or assigned by Subcommittee D24.41 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.