Discuss the use of 'multi-turn' spiral rings for increasing axial take-up.

Multi-turn spiral rings (2-turn or 3-turn) provide a $360^{\circ}$ retaining surface with no gaps, which is superior for uniform load distribution compared to single-turn rings. They are often used to take up axial play in an assembly. By selecting a specific thickness $T$, the ring acts as a rigid shim. In assemblies with high axial tolerances, 'Laminar' rings (multiple rings stacked) can be used, although a single multi-turn ring is usually preferred for ease of assembly. The multi-turn design also increases the centrifugal capacity, as the turns support each other against radial expansion.