GASCO 482 Calibration Gas, Carbon Monoxide 50 PPM, Methane 25% LEL, Hydrogen Sulfide 25 PPM, Oxygen 12%, 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