GASCO Calibration Gas 74-405x-2.5-CO2-2.5-CH4 Mixture CH4 2.5% (50% LEL), CO2 2.5%, CO 500 PPM, H2S 50 PPM, Balance Nitrogen Contained in a 74L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA