... internal Glycerin filled Back connection Good quality Liquid filled Pressure Gauge:Case sizes: 1.5", 2", 2.5", 3", 4" and ... ", 3/8", 1/2", BSP, NPT or BSPT dependent on model and size; bottom, back, left and right side connection Available ... .5% accuracy, U-Clamp, restrictors. back connection glycerin filled Pressure Gauge