The Dwyer Magnehelic gauge is the industry standard to measure fan & blower pressures, filter resistance, air velocity, combustion chamber draft & more. Pressure limits ‑20"Hg - 15 psi. Temperature limits ‑7°C to 60°C. 4" diameter dial. Mounting orientation: diaphragm in vertical position. Connections: ⅛" female NPT, 1 pair at side & 1 at rear.