GASCO 650es-417BS Calibration Gas, 50 PPM Carbon Monoxide, 10 PPM Hydrogen Sulfide, 0.7 % Pentane (50 % LEL), 18 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA