GASCO Precision Calibration Gas 650es-463X Mixture 25 PPM Hydrogen Sulfide, 2.5% Methane (50 % LEL), 19% Oxygen, 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