I have an old article that explains the pole construction shown in the series of pictures posted in the "hunts and finds" folder that begins here. [id=188408338] The text explains as transcribed below (sorry about the all caps, that is the way it scanned in).
"MANY DIFFICULTIES WERE EXPERIENCED WITH THIS LINE WHERE IT CROSSED ALKALI FLATS AND UNDER CERTAIN CONDITIONS A CONDUCTING SUBSTANCE WAS DEPOSITED ON THE UNDER PETTICOATS OF THE INSULATOR AND ON THE PINS UNTIL THE LEAKAGE TRAVELING OVER THE CROSSARM TO THE STEEL BRACE CREATED A SUFFICIENT HEAT TO SET THE POLES ON FIRE WHEREVER THE STEEL CAME IN CONTACT WITH THE POLE. THIS CONDITION WAS IMPROVED BY THE USE OF TREATED WOODEN BRACES; HOWEVER, AN ALMOST COMPLETE CHANGE IN DESIGN WAS MADE BY MORTISING THE CROSSARM THROUGH THE POLE, USING HARD WOOD PINS THROUGH POLE AND CROSSARM, ALSO THROUGH THE ARM AND INSULATOR PIN. IN FACT, NO METAL, NOT EVEN A NAIL, EXCEPT THE CONDUCTORS WAS TO BE FOUND ON THE POLE. THIS DESIGN, WITH LONGER TREATED PINS WAS IN USE BY THE TELLURIDE COMPANY UNTIL THE INTRODUCTION OF THE SUSPENSION INSULATOR. THIS FIRST 40,000 VOLT LINE WAS COMPLETED DURING THE FALL AND EARLY WINTER OF 1897."
The article also mentions
"THE INSULATOR WAS OF THE CONVERSE DESIGN 9 INCHES IN DIAMETER WITH THREE LEAKAGE RIBS BETWEEN THE PIN AND THE OUTSIDE PETTICOAT."
This photo above is actually from a different article, but it covers the same subject and shows the pole nicely. It dates from 1905.