GASCO 44es-411 Calibration Gas Carbon Monoxide 100 PPM, Pentane 25% LEL, Hydrogen Sulfide 25 PPM, Oxygen 19%, Balance Nitrogen contained in a 44L Liter Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA