Calibration Gas, 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 0.35 % Pentane (25 % LEL), 18 % Oxygen, Balance Nitrogen contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection: 330 Gas Specific, Calibration Certificate NIST, Made in the USA