GASCO 411A Calibration Gas, 100 PPM CO, 25% LEL Pent. (.35% vol.), 25 PPM H2S, 20.9% O2, Balance Nitrogen 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