When reading fuel pressure, keep in mind that a fluid filled pressure gauge will change it's reading as the temperature of the gauge case changes (under hood temperature). because it's sealed to contain the liquid inside, a liquid filled gauge no longer compares line pressure to actual atmospheric pressure, reporting the difference. Instead, it compares line pressure to the pressure inside the gauge case. As the liquid in the case heats or cools, it expands and contracts, causing case pressure to change as much as 1 PSI for every 30 degrees temperature change of the gauge. Features 1/8 in. Npt male thread on back of gauge.