Like the alley arm construction poles, those poles with a construction of at least one horizontal insulator holder and at least one vertical insulator holder, or constructions with at least two horizontal insulators holders whenever there is at least one on the opposite side, also do not have wires that end on one side and begin on the other side, with looped wires that connect the electricity going through.
The standard crossarm construction that show the left and right wires being on the ends, while the middle wire is held up with a vertical insulator, seems to be the standard since the late 1970's and early 1980's. At least that's when I first recall seeing such a construction.
I've seen some instances in which two straight-shaped insulator holders are screwed on across from each other on the pole, in which a bolt is also holding them together, and that one of these holders does not have an insulator on it. I am guessing that doing this type of construction for the insulators and holders was probably more common back in the late 1970's and early 1980's, some of which are still there today.
There seems to be a pattern as to which side the vertical insulator holders are on, especially on newer poles. These insulator holders seem to be fastened on the opposite side of where the road is. The exception, however, are those poles that have either a push brace pole or stub pole.
Years ago, crossarms made had wooden insulator pins that simply push into premade holes. Nowadays, the insulator pins appear to be metal rods that screw into the holes of a crossarm.
There have also been certain wooden pins of the past that actually have screw-like threads on them.
Over the years, sometimes a wooden pin can fall through a premade hole a bit more, sticking out at the bottom of the crossarm. This is probably as a result of the wood changing over the years.
Insulators were smaller and dark brown or black years ago. Nowadays, they are gray and bigger.
Insulators that date even further back were more transparent looking, usually colored blue or are of no color.
The material used to make insulators has changed over the years. Years ago, they were made of glass, then were made out of ceramic material; today, they are made of plastic.
Many of the old glass insulators that are still in service are on smaller crossarms lower on the pole, crossarms that usually hold one or two very thin wires, which are possibly used by the local fire department.
On some newer crossarm constructions where the wiring goes off in a different direction (such as when the wires cross the road), the insulators appear as if they are leaning. These insulators seem to be on special pins that make them appear this way. The reason for this is probably because of more pressure than usual from the wires.