This paper presents a cross-section of the various types of PTO's available today. Factors to be considered in selecting a good transmission and PTO combination are pointed out. Particular attention is paid to the most common PTO used in mobile equipment, the SAE six-and eight-bolt version. Physical construction, mounting to the transmission, shifting, bearings, gears, capacity, and controls are examined. Engine speed range and the pitch-line velocity method of evaluating transmissions offer a way of judging performance.