Official Answer
Answer
In a perfect theoretical model, grooves have $90^\circ$ sharp corners. In reality, tools have a radius $R$, and the mating component often has a chamfer $C$. These features reduce the effective contact area between the ring and the groove wall. The thrust capacity must be derated using a factor $K$. If the chamfer on the retained part is too large, it creates a 'wedge' effect that tries to expand the ring (bore type) or contract it (shaft type) out of the groove. As a rule of thumb, the maximum allowable chamfer or radius is $0.5 \times d$ (groove depth). If the chamfer exceeds this, a backup washer must be used to provide a square face for the ring.
