General Order 64-A
Strength Requirements For All Classes Of Lines
Insulators, supports, clamps and other miscellaneous attachments shall be designed to withstand with at least the safety factors, the mechanical stress to which they are subjected by conductors, wires or structures, under the loading conditions as specified in Rule 43. Pin insulators shall effectively engage the thread of the pin for at least two and one-half turns.
Guy insulators, including insulators in messengers, shall have mechanical strength at least equal to that required of the guy wires in which they are installed.
C. Replacements (see Rule 44.2)