GASCO 552L-BTEX Calibration Gas 1 PPM Benzene, 10 PPM Toluene, 10 PPM Ethylbenzene, 20 PPM m-Xylene, 20 PPM o-Xylene, Balance Air contained in a 552 Liter Disposable Steel Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection: CGA 590, Calibration Certificate NIST, Made in the USA