>>51773Not OP, but as far as I understand:
An indicator showing that that area is "Filled in", not open or dug out.
Yes.
I found a ton on Ebay with a quick google.
The two round things and dotted lines are a failed attempt at an orthographic view, a viewing of an object from a certain benchmark angle, for use in manufacture by engineers and stuffs. Concealed elements, such as holes within the assembly, are represented with dotted lines. (It's a top down view.) It's failed because the lines are supposed to be straight and it's really rustling my jimmies.
