GASCO 400 Calibration Gas 250 PPM Carbon Monoxide, 15 PPM Hydrogen Sulfide, 2.5 % Methane (50 % LEL), 18 % Oxygen, Balance Nitrogen in a 650 Liter, For Use with Any and All Gas Detectors, Cylinder Connection: TBD Gas Specific, Calibration Certificate NIST, Made in the USA