Valves are available in several styles, but as a beginning scuba diver, you only need to be familiar with the three common styles. These are the "K" valve, "J" valve, and DIN valve.

"K" valves are the simplest of all valves, and are found on most modern cylinders. These valves fit regulators with yoke attachments. The regulator is attached by slipping the yoke attachment over the valve and tightening a screw against the rear of the valve.

The o-ring on a "K" valve is expanded by air pressure, and this expansion creates the seal between the regulator and valve. Over time, the o-ring may crack, wear out, or fall out, so it should be inspected before attaching the regulator.