Looks like piece of a wheel and an axle from a tractor or a truck or something.
Marking the exact center of France
i remember seeing somewhere in paris the prime pin
must be around Notre Dame
edit: yes, it indeed is there : point zéro
At the beginning of the first world war they plotted all military operations using these giant pins. Later in the conflict ‘map pins’ were developed and these ‘land pins’ became obsolete. Another fascinating example of how the horrors of war pushed technology forwards in civilian applications.
It looks very rough, it could be an unfinished part: a fusion that hasn’t received the subsequent machining.
Maybe a flywheel.
I think that’s just from many years of rust and wear. I doubt that’s the original surface finish