Answer
Internal rings are compressed for installation into a bore, while external rings are expanded for installation over a shaft. This difference dictates the tool geometry. For internal rings, the tool must have a 'contraction' mechanism (like a conical funnel) that reduces the ring's diameter. For external rings, a 'spreader' tool or a tapered mandrel is used to increase the diameter. The design of these tools must ensure that the 'Maximum Deflection' $f_{max} = D_{free} - D_{installed}$ does not exceed the material's elastic limit. Furthermore, the tool's contact surface must be smooth to avoid scratching the ring's edges, which are the most vulnerable points for crack initiation. For multi-turn rings, the tool must also prevent the turns from 'spiraling out' or overlapping during the expansion/contraction phase.
