Metal poles were commonplace for trolley service because of their very heavy direct-current cables (often 600V) that they carried. Many similar poles still are in active use in Boston, MA along with wooden crossarms and angled crossarm braces suporting them like you see here. They utilize large saddle-groove porcelain insulators as well as some older bakelite side-mounted pintypes (fyi...no CD 140 Jumbos or other glass pintypes).