GASCO 427A Calibration Gas 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.25 % Methane (25 % LEL) , Balance Air (20.9 % Oxygen balance Nitrogen) Contained in a 66L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA