MSA 813720 Calibration Gas Mixture Equivalent by GASCO 2.5% Methane, 300 ppm Carbon Monoxide, 15% Oxygen, 10 ppm Hydrogen Sulfide, Balance Nitrogen, contained in a 58 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA