These are three different models of "Peranella" threadless. The white model is probably the oldest and is marked Ginori incuse (probably late 1800, early 1900), while the brown models are not marked and probably less old. (From past swaps with my friends Christian and Guido, thanks!).

It is not easy to date precisely this type of insulator because some brown models, were also retrieved on buildings built in the '30s. The most likely hypothesis is that, probably, at least in Italy, 90% of the oldest insulator that we see today is not in its "original" position, but recycled and replaced after dismissions of the old telephone and telegraph lines. Times were different and there was no consumerism ...