The ratchet-and-pawl design arrests movements by employing a small gravity- or spring-actuated lever paired with a notched wheel.
The lever is jammed between the back of the notch and its pivot point, stopping movement in that direction against any force that the materials used can withstand.
The wheel has little resistance moving in the direction desired, other than that required to lift or push the lever over the next notch.
To resist movement (or when creating incremental steps), methods are employed which include a spring-loaded ball detent that locates in small incremental depressions, or a piece of spring steel that snaps into position on flat surfaces or shallow notches milled into the shaft or wheel.
Stepper motors rely on magnetic detents to retain step location when winding power is removed.