46 CFR §56.25-20

1. (a)
   1. (1)Bolts, studs, nuts, and washers must comply with applicable standards and specifications listed in § 56.60-1. Bolting must be in accordance with ASME B16.5 (incorporated by reference; see § 56.01-2).
   2. (2)Bolts and studs must extend completely through the nuts.
   3. (3)See § 58.30-15(c) of this subchapter for exceptions on bolting used in fluid power and control systems.
2. (b)Carbon steel bolts or bolt studs may be used if operating pressure does not exceed 300 psig and the operating temperature does not exceed 400 °F. Carbon steel bolts must have heavy hexagon heads in accordance with ASME B18.2.1 (incorporated by reference, see § 56.01-2) and must have heavy semifinished hexagonal nuts in accordance with ASME B18.2.2 (incorporated by reference, see § 56.01-2).
3. (c)Alloy steel stud bolts must be threaded full length and use heavy semifinished hexagonal nuts in accordance with ASME B18.2.2.
4. (d)Alloy bolts or studs and nuts are to be threaded in accordance with ASME B1.1 (incorporated by reference; see § 56.01-2), Class 2A external threads, and Class 2B internal threads (8-thread series 8UN for one inch and larger).
5. (e)(Reproduces 108.5.1.) Washers, when used under nuts, must be of forged or rolled material with steel washers being used under steel nuts and bronze washers under bronze nuts.