An exemplary knob assembly includes a knob having a circumferential channel, and a deformable ring seated in the circumferential channel. The ring is normally rotatable relative to the knob such that rotation of the ring does not cause a corresponding rotation of the knob. When gripped with a sufficient gripping force, the ring frictionally engages and rotationally couples with the knob, thereby permitting transmission of torque between the ring and the knob. In certain embodiments, the knob assembly may include a detent mechanism operable to selectively couple the ring and the knob. In certain embodiments, the ring may include protrusions operable to engage pockets in the knob to provide for rotational coupling.