GASCO Precision Calibration Gas 650es-404-17X-SO2 Mixture Methane 50% LEL, Oxygen 17%, SO2 10 PPM, H2S 25 PPM, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA