GASCO Precision Calibration Gas 116L-424-17 Mixture 50% LEL Methane, 17% Oxygen, 100 ppm Carbon Monoxide, 10 ppm Hydrogen Sulfide, Balance Nitrogen Contained in a 116L Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA