What is considered the bead in this diagram? I'm trying to understand wheels better and I googled Bead Seat Diameter and this image comes up a lot ...



There are two components that look to be the exact same with one flipped vertically.

Here is a picture of a 20 inch wheel for example:



What is considered the "bead"?  Is it that little circle.  A bead is normally just one small item on a necklace ( google ).

But in this case if it is that little circle, would the bead be something that creates a torroid and goes around the entire wheel?

From what I can tell the tire and the spokes are not depicted in the diagram, just the "metal" frame cross section.
The bead is the wire at the inner edge of the tire, which creates a bulge in the edge that locks into the groove in the rim. The word "bead" here is more akin to the woodworking term bead than to the "small ornaments on a string" sense.