Scuba Cylinder Markings
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.
Many countries, including the United States, require a cylinder to be approved by a government agency. Cylinders used in the United States must be approved by the Department of Transportation (DOT). Cylinders manufactured before 1970 will have the letters "ICC" instead of "DOT."