GASCO Precision Calibration Gas 34L-429ST Mixture 25% LEL Methane, 15% Oxygen, 200 ppm Carbon Monoxide, 75 ppm Hydrogen Sulfide, Balance Nitrogen Contained in a 34 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA