GASCO Calibration Gas 650es-487TBS-M Mixture 50 PPM Hydrogen Sulfide, 0.9 % Butane (50 % LEL), 18 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA