GASCO 34es-411 Calibration Gas Mixture: 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 0.35 % Pentane (25 % LEL), 19 % Oxygen, Balance Nitrogen contained in a 34 Liter Factory Refillable ecosmart Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection C-10 5/8"-18 UNF, Calibration Certificate NIST, Made in the USA