The fctory blocks with tabs to hit the bump stops are cast, but on my trucks .... the saddle that's welded to the axle tube, most often called a "spring perch" ... is not cast anything.

They're stamped and formed from plate steel, and are about 1/4" thick.

Look on top of the axle, under the blocks.

The lower one isn't welded to the axle tube, it's part of the clamps that hold it all together in a stack.