GASCO 403EX Calibration Gas, 1.62% vol. Methane (50% LEL Prop. equiv.), 25 PPM H2S, 18% O2, Balance N2 contained in a 66L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA