GASCO 490 Calibration Gas, Carbon Monoxide 35 PPM, Methane 10% LEL, Hydrogen Sulfide 10 PPM, Oxygen 18%, 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