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. Movement Brass, Case Material Black enameled steel, Max. PSI 30, Accuracy Grade B, Mount Type Back, Connection Size in. 1/4 Male NPT, Pointer Aluminum, Window Material Acrylic, Dial White Aluminum, Gauge Diameter in. 2 1/2, Range PSI 0-30, Recommended Use Air, gas, oil, water, Bourdon Tube C-shaped.