Kim,
I would assume the cup was mostly decoration, especially to hide the ugly rear of the gauge for outside mounting. Being pointed I suppose there might be an aerodynamic advantage. There would have to be holes in the bottom of the cup for wires or lines to the gauge.
This may be what you're looking for. It's from a 1968 Midwest catalog. No brand name is mentioned but everything else in the column is S/W.
Verne
