GASCO Calibration Gas 650es-414WI Mixture 300 PPM Carbon Monoxide, 10 PPM Hydrogen Sulfide, 0.81 % Pentane (58 % LEL), 15 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection TBD, Calibration Certificate NIST, Made in the USA