Answer
The retained part (the component being held in place) often has a chamfer or a radius on its edge for manufacturing ease. However, this chamfer creates a 'ramp' that exerts a radial component of force $F_r = F_a \tan(θ)$ on the retaining ring, where $F_a$ is the axial force and $ heta$ is the chamfer angle. This radial force tends to push the ring out of the groove. If the chamfer is too large, it can cause the ring to 'dish' and fail prematurely. The maximum allowable chamfer or radius on the retained part is typically specified in the ring's technical data sheet (e.g., $r_{max} < 0.5 \cdot d$, where $d$ is the groove depth). If a large chamfer is unavoidable, a 'square-edged' backup washer must be used to ensure the load is applied purely axially to the ring's face.
