This is an old banjo flange made I believe of cast aluminum (?). It is non magnetic and weighs 2 & 1/2 lbs. It has cracks as shown in the photos but is solid with no movement of flaking.
It measures 10 & 3/4ths inches from inner edge to inner edge, 11” outer edge, and 13&3/8” outer edge to outer edge.
It is heavily patinated and would need some cleanup. I don’t know what instrument it came from of much of anything else. Perhaps a ebayer can let know and if that happens I will update the description.
The photos show some details. Text with questions, information or offers .
Winning bidder to include $12.95 for s&h.