Bilstien front shocks and coil springs.

So I think i got most of this figured out, I'll get the top caps for the coils from Toyota, the rest of the bushings should come with the shocks. What i need to know is what is this bottom piece circled in yellow?
i don't see it on the shock itself from the Bilstien website, unless it that large round black piece. Anyone familiar what this is?

 

The black ring is the lower spring perch. You can see it mounted on the shock in the smaller view.

 

The top caps don't wear, but the 4600s only come with one cushion so try to find another. There's no reason to change them unless you want the shock assembled and separate.

They are the dark thick circle in the picture.