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