GASCO 600L-135A-2.5 CH4 2.5% Volume (50% LEL) Calibration Gas in Air contained in a 600 Liter Aluminum Disposable Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection: CGA 590, Blend Tolerance +/-5%, Analytical Tolerance +/-2 Calibration, Calibration Certificate NIST, Made in the USA