GASCO 411-TBS Calibration Gas, 100 PPM CO, 25% LEL Pent. (0.35% vol.), 15 PPM H2S, 18% O2, Balance Nitrogen contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection: TBD Gas Specific, Calibration Certificate NIST, Made in the USA