The post hole auger is an attachment that can be driven by either a hydraulic motor, or a PTO driven gearbox. They can be mounted on skid steer loaders using a universal quick attach connection, or on the back of a tractor using the common 3 point connection that can be found on almost every tractor. In addition to being able to mount post hole augers on almost any piece of machinery, there is also a version that can be held by one or more people by hand for smaller applications. Augers are also available in non-machine driven varieties, which would not be very effective for the purpose of making post holes.
Augers are rated for two things. The power they provide, and the maximum size bit they can effectively turn in the ground. Skid steer augers have their power rated by how much hydraulic fluid is needed to pump through the motor every minute, which directly affects the RPMs at which they turn. Tractor post hole augers are rated in horsepower based upon how much horsepower the gearbox located at the top of the assembly is rated to withstand.