GASCO Calibration Gas Mixture: 50 PPM Carbon Monoxide, 50% LEL Methane, 10 PPM Hydrogen Sulfide, 18% Oxygen, Balance Nitrogen, Contained in a 44 ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection C-10, Calibration Certificate NIST, Made in the USA