Answer
Crest-to-crest, nested, and interlaced.
- Crest-to-crest — turns in series, crest resting on crest. Gives the lowest spring rate and the widest usable deflection for a given height, and covers most applications.
- Nested — turns in phase and in parallel, for maximum load where the space is already fixed.
- Interlaced — two coils wound together to reach a spring rate that neither would achieve alone.
The choice follows from whichever constraint is already locked. Fixed space with a high load points to nested; a fixed load that needs travel points to crest-to-crest. Anything outside those two is worth discussing with the manufacturer before the cavity is machined.