CH4 Calibration Gas in Air contained in a 58 Liter Aluminum Disposable Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA
FOR 50% LEL METHANE USE
https://www.calgasdirect.com/gasco-103l-135a-2-5-calibration-gas-50-lel-methane-2-5-volume-balance-air-103-liter-cylinder-c-10-connection/