GASCO Precision Calibration Gas 58L-0.6% Propane, 50 ppm Carbon Monoxide, 19% Oxygen, Hydrogen Sulfide 15 ppm, Balance Nitrogen Contained in a 58L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA