Mechanically all the illustrated items are variants of the nut and bolt [123387].
The heads are larger, and so act as washers to spread the strains.
The heads are thin, since they do not need the strength normally required from plain nuts and bolts.
The head of the bolt extends to be a sleeve to cover the thread of the nut. Once in use the sleeve is out of sight anyway. This protection of the threads causes less wear on pages when a book is in constant use.
They are invariably designed to fit the standard office paper-punch size of 5mm.
They are made in a variety of metals and plastics. We show brass ~ nickel plate ~ white plastic (probably nylon).
They come in a variety of internal lengths ~ typically 2 ~ 3.5 ~ 5 ~ 10 ~ 15 ~ and more.
Extenders are available, typically 5 ~ 10 ~ 15.
Here is the code for a link to a local USP [116537]