GASCO Calibration Gas 74-403S Mixture 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.62 % Methane, (32.4 % LEL), (50 % LEL Propane Equivalent), 19 % Oxygen, Balance Nitrogen Contained in a 74L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA