GASCO 411S Calibration Gas, 100 PPM CO, 25% LEL Pent. (0.35% vol.), 30 PPM H2S, 19% O2, Balance Nitrogen contained in a 44L 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