GASCO Calibration Gas 66es-414-35 300 PPM Carbon Monoxide, 35 PPM Hydrogen Sulfide, 1.25% Methane, (25% LEL), (50% LEL Pentane Equivalent), 15% Oxygen, 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