Stamped on the tool is the following......"ALFA ROMEO D'ASS"
½ " square drive one end with what looks like a 15 mm offset ring spanner end on the other.
Photo attached.
I vaguely recall buying this from an AR dealership in the 80's.
I believe it may be the special AR tool for adjusting the De Dion rear on an Alfetta but cannot be sure.
There are other stamped numbers on the tool, but they are almost impossible to read.
Cheers