Why you need this? "Compared to an air filled gauge, the glycerin pressure gauges are our preferred gauge. It will be much quieter as water has a tendency to vibrate when running, as well as lasting much longer as the oil in the gauge will soak up the vibrations which can cause excessive wear on air filled gauges. Sufficient PSI is very important for the correct operation of a reverse osmosis unit. Low water pressure is a leading cause of poor RO system performance. A pressure gauge assures that proper pressure is being supplied. It will also make pressure drops apparent which can tell you that sediment and carbon blocks need to be changed. Glycerin filled pressure gauges absorb vibration and pressure spikes increasing service life. This glycerin filled pressure gauge comes with 1/4" quick connect fittings for quick easy installation in-line before the RO Membrane." Notes regarding glycerin-filled meters There is an air bubble in the glycerin that you can see, and it is there by design. If there is no bubble, the meter is faulty. There is no need to cut the rubber plug on the top of the meter as that will open the meter to possible infiltration of particulate contaminants and moisture, as well as allow the glycerin to leak out How to use it? Assemble the gauge as photo show, then pop in your 1/4" tubing into each end of the Tee , and finally keep the gauge standing up right with teflon tape or zip ties. To remove, just push in the outer circle on each end and pull right out. You need to make sure the tubing is cut squared to insure no leaks.Be sure you tighten the plastic fitting connected to the gauge by an adjustable wrench What you will receive? Gauge x11/4" NPT to 1/4" push-to-connect adapter x 11/4" Union Tee x1