What is this clamp called? pic inside

tia

http://mywebpages.comcast.net/jrt404/cav.jpg

The one on the other side rusted thru, so I'll need to replace both.

Rusted?
I see no use for it other than it may be an ID tag for the frame plant build.

What does it clamp?, I can not tell from the pic.

The clamp holds the rear sway/tortion bar to the axle. Without the clamp there, every bump causes a rattling sound.