GASCO 502 Calibration Gas Mix, 0.9 % Methane, 0.9 % Ethane, 0.9 % Propane, 0.9 % Iso-Butane, 0.9 % Butane, in N2 contained in a 17 Liter Disposable Steel Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 600, Calibration Certificate NIST, Made in the USA