A mechanism for adjusting the relative angular orientation of two coaxial components includes a mandrel having a cylindrical central section between upper and lower splined sections, a sleeve rotatably and slidably disposed around the mandrel's central section, and generally cylindrical upper and lower ratchet members positioned, respectively, about the mandrel's upper and lower splined sections. The ratchet members have internal grooves which receive the mandrel splines for torsional load transfer while permitting limited rotation relative to the mandrel, but their axial positions relative to the mandrel are fixed. The upper and lower ends of the sleeve have circumferentially-arrayed ratchet teeth engageable, respectively, with corresponding teeth on the upper and lower ratchet members. The central sleeve has torque-transferring external splines slidable within matching grooves on the inner surface of a cylindrical tool housing enclosing the mechanism. The mandrel is rotatable relative to the housing, but its axial position is fixed. The teeth of the sleeve and ratchet members are configured such that movement of the sleeve from a position engaging the upper ratchet member to a position engaging the lower ratchet member, or vice versa, will effect an incremental angular shift of the mandrel relative to the tool housing, while maintaining effective transfer of torsional loads therebetween.