In rotary drilling, a crew rotates a bit that drills a hole through the earth in search of oil or gas. The crew attaches the bit to a hollow length of pipe that serves two purposes: it provides the weight to make the bit dig into the earths formations, and it provides a passageway to circulate a fluid--drilling mud--to the bit as it rotates. As the crew drills deeper into the earth, crew members add more pipe to the pipe already connected to the bit. Before a well is completed, this drill stem may be thousands of feet long.Because the drill stem serves two purposes, it consists of, among other things, two basic types of pipe: the drill string and the drill collars. This training manual teaches rig personnel about these two types of pipe and helps readers to understand pipe design, function, failures, maintenance, and inspection. Readable language, clearly labeled illustrations and photographs, a glossary, and helpful self-test review questions help the reader to comprehend the material.This lesson replaces The Drill Stem in the series.