GASCO 552L-311-18 Calibration Gas 100 PPM Carbon Monoxide, 0.35% Pentane (25% LEL), 18% Oxygen, Balance Nitrogen contained in a 552 Liter Disposable Steel Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection: TBD GAS Specific, Calibration Certificate NIST, Made in the USA