This is a late war-early 20’s enlisted Type II disk.
This bold diamond grid with dots is the Type II pattern which came into use during the late WWI era, and worn to 1923. Superimposed over the grid is a regulation 1917 Air Service wings and prop insignia. Has a thumb nut that likely is a replacement.
Very good- fine condition with wear on the high spots only, mostly on the wings and prop.