GASCO 421-17 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 2.5 % Methane (50 % LEL) , 17 % Oxygen, 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