Toronto. When it comes to accessories for the Leica, the ZOOXY and its brethren are right up there as candidates for the ugly prize. The massive weighty thing is a focusing mount and extension tube that connects to an OOZAB focussing stage. It focuses a 5cm Elmar from 1m to 23cm (about 9 inches) using the Elmar’s bayonet and not its screw-mount threads. It was available from around 1951.
The mount was later made with the much wider 51mm thread mount for the last run of focussing stages. It seems to be made of brass (it’s non magnetic) with a durable black enamel coating. If you were to drop it, I think the floor would suffer the damage, not the ZOOXY!