Code of Federal Regulations Title 29. Labor § 29.1919.16 Heat treatment

(1) Half-inch and smaller chains, rings, hooks, shackles and swivels in general use, at least once every six months;  and

(2) All other chains, rings, hooks, shackles, and swivels in general use, at least once every twelve months.

(3) In the case of gear used solely on lifting machinery worked by hand, twelve months shall be substituted for six months in paragraph (a)(1) of this section and two years for twelve months in paragraph (a)(2) of this section.

(4) When used in this paragraph, the term “in general use” means used on fifty-two or more days in a year. In any case, however, the period between annealings shall not exceed two years.