1 CFR § 21.11 - Standard organization of the Code of Federal Regulations.
The standard organization consists of the following structural units:
(a) Titles, which are numbered consecutively in Arabic throughout the Code;
(b) Subtitles, which are lettered consecutively in capitals throughout the title;
(c) Chapters, which are numbered consecutively in Roman capitals throughout each title;
(d) Subchapters, which are lettered consecutively in capitals throughout the chapter;
(e) Parts, which are numbered in Arabic throughout each title;
(f) Subparts, which are lettered in capitals;
(g) Sections, which are numbered in Arabic throughout each part. A section number includes the number of the part followed by a period and the number of the section. For example, the section number for section 15 of part 21 is “§ 21.15”; and
(h) Paragraphs, which are designated as follows: