29 CFR 1919.16: Heat treatment.

(a) All chains (other than bridle chains attached to derricks or masts), rings, hooks, shackles, and swivels made of wrought iron, which are used in hoisting or lowering, shall be annealed in accordance with § 1919.36 at the following intervals:

(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.

(b) Chains, rings, hooks, shackles, and swivels made of material other than wrought iron or steel shall be heat treated when necessary in accordance with § 1919.36(b).