"2.5in. dry back-mount gauge has brass movement with C-shaped Bourdon tube. 1/4 male NPT male connection. Grade B accuracy. Designed for use with air, gas, oil or water. Black enameled steel case, aluminum pointer, white aluminum dial and acrylic window. Bourdon Tube C-shaped, Movement Brass, Recommended Use Air, gas, oil, water, Case Material Black enameled steel, Connection Size in. 1/4 Male NPT, Range PSI 0-30, Accuracy Grade B, Window Material Acrylic, Pointer Aluminum, Dial White aluminum, Gauge Diameter in. 2 1/2, Product Type Gauge, Mount Type Back, Max. PSI 30."