Discuss the effect of 'Groove Fill' on the stability of a spiral retaining ring.

'Groove Fill' refers to the percentage of the groove's radial depth occupied by the ring. A high groove fill (over 90 percent) ensures maximum stability and resistance to 'dishing'. However, enough clearance must remain to allow for ring contraction/expansion during installation. In applications with high radial loads, like heavy-duty universal joints, we specify a 'tight' groove fill. If the groove is too deep and the ring too narrow, the ring may shift radially under load, leading to an imbalance and potential vibration-induced failure of the assembly.