The gauge is liquid filled with a light oil to eliminate the needle from vibrating so an accurate pressure can be read. The air bubble is there on purpose, so you know the oil is present.

Nostalgic look with Black Face and the famous Mooneyes Logo. Chrome bezel. 1-15 PSI is suitable for most 4 barrel carb set ups. 

The gauge has a 1/8" NPT male connection.  Other fittings will be required to fit but they are not included in this listing.