This description is from an early electrical supply catalog: Holmes Tree Insulators prevent leakage, short circuits and tree grounds. Made of malleable iron with double petticoat insulator. Always in upright position regardless of slant of tree. Current cannot leak even if wire is bare. It can be applied quickly without cutting the wire. Style A takes wire up to 00 B. & S. Style B takes wire up to 0000 B. & S.