The forementioned hardware was made by the St. Louis (STL) Malleable Company and was used almost exclusively by the Union Electric Company from about 1900 through the following several decades. They produced all manner of insulator pins, brackets and whatever else a utility might need when it came to being made of high-quality metal. Note the unusual "spreader" brackets on the lower crossarm.

Phone and municipal services openwire lines are upon the three crossarms above.