GASCO 34es-428-20 Calibration Gas Carbon Monoxide 60 PPM, Methane 1.45%Vol = (58% LEL) Pentane simulant, Hydrogen Sulfide 20 PPM, Oxygen 15%, Balance Nitrogen contained in a 34 Liter Factory Refillable ecosmart Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA