GASCO 309SP-1.25 Mix, 200 PPM Carbon Monoxide, 1.25% Methane (25 % LEL) 19 % Oxygen, Balance Nitrogen Calibration Gas, 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