Does anyone know what this visible part goes to? Please and thanks, Steve

OD - 18 1/2”
ID - 10 1/8”
Cylinder - possibly 12 1/2”

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-Steve B. (WTB: 48" Flying A button, 48" black/org Phillips 66, White Star, and Chevrolet Signs. Also looking for a Wayne 866. Send a PM. Thanks.)