Engaging inclined surfaces of an inner ring and an outer ring create wedge action inducing an inward radial force as the rings are forced together longitudinally, holding the adjustor on a rotating body. An inner total arcuate length of each ring is smaller than an outer total arcuate length of a respective target body (inner ring for outer ring, rotating body for inner ring). Arcuate segments of each ring can have inner surfaces with radii of curvature equal to or smaller than that of the target body outer surface, and with a total arcuate length smaller than the circumference of the target body's outer surface.