That hardware needs only one hole in wall to install two insulators and connect telephone to building. In 1950s and 60s in Warsaw was many that type hooks. Sometimes hooks was installed near windows on big buildings (from 0 floor to 5th floor) and wires goes from pole straight to window and next to flat.

On that one is one typical glass insulator, and one porcelain from germany (closter velisdorf). I planned to install that at home like as halogen light wire holder.