A Stainless Steel 100mm Liquid Filled Bottom Entry Pressure Gauge is a Pressure Gauge with a 100mm face on it (the face is what you can read). It is made out of 304 Stainless Steel housing with brass entry and internals and is filled with glycerine which is what we called liquid filled. The connection to the media or what we called entry is on the bottom of the pressure gauge. All liquid filled pressure gauges have an air bubble that you can see on the face, this just helps when the air pressure changes in the environment it wont force some of the liquid out of the dial.