GASCO Precision Calibration Gas 650es-428-20MBS Mixture 60 PPM Carbon Monoxide, 20 PPM Hydrogen Sulfide, 0.375 % Pentane (25 % LEL), 15 % 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