Any idea what this is? I was removing the Z-bar and clutch rod from the driver's side of my 1970 'Cuda. As I removed the large nut from the fender side of the Z-bar, the washer fell off onto the frame rail. As I felt for the washer, I knocked this off the inner frame rail onto the floor. I don't know where it came from as the center hole is too small to fit the Z-bar bolt. And I don't know if it came off today or has been sitting in the frame rail for a while. It is 1 3/8 inches in diameter, 1/8 inch thick. One side is flat like a washer, the other side is convex (slightly domed). It has a 3/8 inch center hole that is squared off on one end. It is too small to be the adjuster for the upper control arms. Any help would be appreciated.