If hooks are used to attach cages or buckets to the socket or thimble of a hoisting rope, the hooks shall be self-closing.
30 C.F.R. §77.1907
Sec. 101, Federal Mine Safety and Health Act of 1977, Pub. L. 91-173 as amended by Pub. L. 95-164 , 91 Stat. 1291 (30 U.S.C. 811 )