Test gas in refillable "Ecomini" cylinder with 18.0 vol.% oxygen (O2) in nitrogen (N2). Approx. 0.85 litre cylinder size at approx. 37 bar Contents: 31.5 litres Connection: IT 5/8"-18-UNF valve connection Please return the empty cylinders to Esders GmbH after use. We will refill them. As a thank you for your contribution to protecting the environment, you will receive a free package of 100 Esders Connect measurements.