I have seen this several times at a local swap. Today I could take it no longer and it came home with me so I could post it here.
Most everything moves one way or another.
The six wedge shaped fingers can be moved rotationally as well as in and out. The one near the 6 o'clock is moved in the next two pictures. The large circular plate can also be rotated.
The marking LM CO Orange Mass appears to hand stamped as do the other markings. The number 3 asks me the question is there a number 1 and 2 size as well? It could equally represent the size of the plate as it measures 2.999. The large screw when loosened allows the plate to be rotated and when tightened locks it.
This is the top edge in the last photo. Another 3.
The edge at the right side in the photos above. The hole is blind and tapped. Looks to my eye like 1/4 20
The reverse side. The screws loosen to allow adjustment of the six fingers.
The other marking 46. Is this a production number? A model number? An operator number?
It is marked Patented so there must have been reason to file a patent but curiously no patent number or date.