Official Answer
Answer
Dish or coning refers to the axial deflection of the ring when subjected to a thrust load. Because a spiral ring is essentially a wound flat wire, it behaves like a very stiff truncated cone under load. The 'Moment of Inertia' of the wire cross-section $I = _x000c_rac{b t^3}{12}$ resists this twisting. If the load is eccentric or the groove is not square, the ring will 'dish' more severely. Excessive dishing reduces the effective shear area and can cause the ring to 'walk' out of the groove. We calculate the maximum allowable load before the ring 'dishes' past a critical angle (usually $7^\circ$) using the formula $M = E I \theta / R$, where $M$ is the applied moment from the thrust load.
