GASCO Calibration Gas 34es-437X-50 Mixture 50 PPM Hydrogen Sulfide, 50% LEL Propane, 18% Oxygen, Balance Nitrogen Contained in a 34 Liter Factory Refillable ecosmart Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA