... Brass internal Glycerin filled Back connection Good quality Liquid filled Pressure Gauge:Case sizes: 1.5", 2", 2.5", 3", 4" and 6" Case ... oil Connection: 1/8", 1/4", 3/8", 1/2", BSP, NPT or BSPT dependent on model and size; bottom, back, left and right side connection ... B40.1 Grade B (3-2-3%) Options and accessories: custom dial, metric scale, DIN 2.5% accuracy, U-Clamp, restrictors. back connection ...