Hard to say exactly what they did without taking it apart, but it kinda looks like the washers might be springs. Concave when loose and flat under tension. That would help to keep the blades close together even after heavy use and wear.
I would assume that the inside face of the bolt has a square or rectangular profile that seats into the hole to prevent it from turning. The nut looks like it was custom made for this use.
The nut and the bolt could be made in small quantities on a metal lathe. For large quantities they would likely be made on a screw machine. The washers are probably an off-the-shelf part but could also be made on a screw machine.
Deal! (i'm swithing to Linux)