Calibration Gas, 10 PPM Carbon Monoxide, 50% LEL Methane, 25 PPM Hydrogen Sulfide, 18% Oxygen, Balance Nitrogen Calibration Gas contained in a 44L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA