81-0154RK-04 RKI Calibration Gas Mixture Equivalent by GASCO, 50 PPM Carbon Monoxide, 50 % LEL Methane, 25 PPM Hydrogen Sulfide, 12% Oxygen, Balance Nitrogen contained in a 34 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA