Chesapeake Black 2' Water Pressure Gauge  (30 PSI) Perimeter-lighted Black dial with stylish Blue and White graphics, polished stainless steel bezel, contoured White pointer and domed glass lens. A pressure gauge operates by sending a low amperage current through the gauges's meter to ground via a sending unit with variable resistance. The resistance of the sending units increase or decrease with the changes in pressure, temperature, etc... As the sender's resistance varies, the amount of current allowed to flow through it to ground changes and the meter deflects, showing the change in pressure. 2' - Hole size: 2.0625' (53mm) Specifications: * Anti-scratch glass lens * Perimeter lighted back light * 12 VDC negative ground * Can be adapted for 24 VDC systems * Dual Scale - Metric and Imperial Factory P/N OP1018 *Sold as an Individual **Gauge Cover not Included