8.—(1) Accessories contributing to the strength of the vessel (for example bolts and nuts) must be made—
(a)of a material specified in paragraphs 2 to 6; or
(b)of other kinds of steel, aluminium or an appropriate aluminium alloy compatible with materials used for the manufacture of pressurised parts.
(2) The materials referred to in sub-paragraph (1)(b) must, at minimum working temperature, have an appropriate elongation after fracture and bending rupture energy.