Be careful when purchasing a Mamiya camera made in the late 1950s.
The focus rings in some were cast from a poor alloy
which develops internal stresses that cause the part to break
apart on its own, as you see in the left half of this photo.
This ring was not smashed. Rather, metals in the alloy didn’t get along together,
causing the ring to self-destruct over the decades.
Camera collectors also see this phenomenon in the sprockets of early Edinex cameras, shutter standards of early Iloca cameras, and in the wind levers of early Pax M3 cameras.
Years ago, I had access to a machine shop, so I made a replacement ring out of brass, seen on the right.
It works well in the camera.
Mamiya’s cameras from back then are attractive, have sharp lenses, and are well made, except for the poor pot-metal in those focus rings. ’Tis a pity.