Fuel Pressure Gauge. 1.5 Diameter. 1/8 NPT Male Connection. 0-15 PSI Pressure Range. Liquid Filled For Durability. Integral Equalizer Valve Ensures Accuracy Regardless of Operating Temperature. Liquid Filled Gauges offer a better looking, more durable option for gauges that will live in a harsh environment like under the hood, attached to a high-performance engine.The problem with regular liquid-filled gauges is they can be temperature sensitive, with fuel pressure readings prone to rising and falling with the temperature of the oil in the gauge case, regardless of actual fuel pressure.As under-hood and therefore gauge temperatures can swing across a large range, this can be especially frustrating. Aeromotive Liquid Filled Gauges feature a custom equalizer valve that allows gauge case to be quickly equalized to the atmosphere, instantly correcting the gauge reading regardless of operating temperature.