CFR > Title 15 - Commerce and Foreign Trade > SUBTITLE B—Regulations Relating to Commerce and Foreign Trade > CHAPTER II—NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, DEPARTMENT OF COMMERCE (parts 200 to 297) > SUBCHAPTER B—STANDARD REFERENCE MATERIALS (parts 230 to 230) > PART 230—STANDARD REFERENCE MATERIALS > SUBPART A—General Information (§230.1 to §230.3) > 230.2—Identification of Standard Reference Materials.

230.2—Identification of Standard Reference Materials.

The SRM's are listed by category in SP 260 and by sequential number in the supplements. The number uniquely identifies a particular SRM. Renewals are indicated by the addition of a letter to the original number. Thus, 11a is the first, 11b the second, and 11c the third renewal of SRM 11, Basic Open-Hearth Steel, 0.2 percent carbon. In this way, a particular number or number and letter always represent a material of fixed or approximately fixed composition.