GASCO 490-T Calibration Gas, Carbon Monoxide 200 PPM, Methane 50% LEL, Hydrogen Sulfide 40 PPM, Oxygen 10%, 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