Abstract: A pressure gauge of small size and type suitable for fire extinguisher use. Comprising the gauge is a dial plate secured in keyed registration onto the front face of the casing. A tubular stem extending laterally from the inside face of the viewing crystal is axially slotted to embrace a radial portion of a wound Bourdon tube supporting a pointer opposite the dial plate. Rotating the crystal prior to securing it to the casing enables the tube slot to zero position the pointer at the zero graduation on the dial plate. When secured to the casing the distal end of the crystal stem compresses an O-ring washer for effecting an internal pressure seal between the casing and Bourdon tube thereat.