GASCO 411EX Calibration Gas, 100 PPM CO, 50% LEL Pentane (0.7% vol.), 25 PPM H2S, 19% Oxygen, Balance Nitrogen contained in a 34 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA