All cylinders have important specifications stamped around the top of the tank. The location and format may vary between manufacturer, but with practice you'll learn to recognize key specifications and what they mean.

All cylinders must pass a hydrostatic test every five years. The test date is permanently stamped on the cylinder if it passes inspection. In this example, the test was performed in June of 2001. A plus "+" symbol following the test date indicates the cylinder can be filled 10% higher than the stated maximum service pressure. Because this test is performed every five years, the cylinder may have several hydro dates stamped on the cylinder.