GASCO 1810-3937 Industrial Scientific Calibration Gas Mixture Equivalent by GASCO 25% LEL Pentane, 25 PPM Hydrogen Sulfide, 100 PPM Carbon Monoxide, 19% 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