A manually operable ratchet mechanism includes a pinion assembly comprised of a handle connected to a shaft. The handle and shaft are mounted on a housing to allow the shaft to be rotated as a consequence of a user manually rotating the handle. The shaft carries a pinion configured to engage a toothed rack to incrementally move the rack in discrete steps relative to the housing. Additionally, a rotatable detent member is provided which rotates with the shaft as the handle is rotated. The rotatable detent member cooperates with a fixed detent member on the housing to define discrete detent positions which provide discrete step tactile feedback to the user. The handle is mounted for (1) axial rotation with respect to the shaft axis and additionally for (2) pivotal movement between locked and unlocked positions around a pivot axis oriented substantially perpendicular to the shaft axis. In the unlocked position, the shaft and rotatable detent member can rotate relative to the housing as the handle is turned. In the locked position, the rotatable detent member is forced into firm engagement with the fixed detent member to prevent axial rotation of the shaft.
