Zenport Zen-Tek Pressure Gauge BLPG100 Zen-Tek 0-100 PSI Back Mounted Liquid Glycerin Pressure Gauge. 0-100 psi Glycerin 'Liquid' Filled Pressure Gauge: 2.5" case diameter, 1/4 NPT, Back Connection, ABS case, 372 plastic window, brass internals and connection. Grade 'A' Accuracy (1.6%)