Olivetti Linea 88
A catalogue of metal characters of 1966
The Olivetti Linea 88 was a office typewriter from Olivetti. It had metal characters, here there is a font with the available fonts.
There are some characters that now are no more in use, other remained, for example Mikron, Eletto, Pica.
The most interesting character here I think it's the perforated one. It was used to prepare the stencil for mimeographs. When doing this stencil, you have to perforate a waxed paper, so to allow the ink to pass through the paper.
One of the problem for example was when typing the letter O.
Since the typewriter had to cut the paper, the risk was that the center of the letter would come off and fall.
But with this perforated character there wasn't this risk.
In the end there is also a diagram with tips on how to use these characters.