GASCO Calibration Gas 74-471-17 Mixture 50% LEL Pentane, 17% Oxygen, 100 ppm Carbon Monoxide, 25 ppm Hydrogen Sulfide, 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