GASCO Precision Calibration Gas 66es-404-17X-SO2 Mixture Methane 50% LEL, Oxygen 17%, SO2 10 PPM, H2S 25 PPM, Balance Nitrogen Contained in a 66L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA