GASCO 17L-17A-0.95 Calibration Gas 0.95 % Butane (50 % LEL), Balance Air (20.9 % Oxygen balance Nitrogen) contained in a 17 Liter Steel cylinder, With a CGA 600 connection. For Use with Any and All Gas Detectors, Cylinder connection CGA 600, Calibration Certificate NIST, Made in the USA