A wave spring is a flat wire coiled edgewise into a helix, with waves (peaks and valleys) pressed into each turn. When compressed, the waves flatten, storing energy just like a coil spring — but in a fraction of the axial length. Swap a coil spring for a wave spring of equal force, and you typically save 50% of the working height. That's why they show up wherever a designer needs preload but has run out of room.

Common types:

• Single-turn — one wavy ring, used as a light preload washer under a bearing or seal.
• Multi-turn (crest-to-crest) — stacked waves nest peak-to-peak, giving higher force in the same envelope.
• Nested — multiple wave spring layers wound in parallel for very high loads.
• Linear (interlaced) — a single continuous coil with waves, giving smoother load/deflection than stacked types.

Where you'll see them: preloading ball bearings in electric motors (removes axial play, kills noise), taking up thermal expansion in aluminum housings, holding clutch plates against a pressure plate, backing mechanical seals in pumps, and inside quick-disconnect couplings. Anywhere a Belleville washer is too stiff and a coil spring is too tall, a wave spring fits.

The force rule of thumb for a crest-to-crest multi-turn wave spring (rectangular wire):

P ≈ (K · E · t³ · f · N) / (D_m³ · b · N_t⁴)

where P is load, E is modulus, t is wire thickness, b is wire width, f is deflection, N is number of waves per turn, N_t is number of turns, D_m is mean diameter, and K is a geometry constant (~3.88 for typical designs). The key takeaway from that formula: force scales with t³ and drops with N_t⁴. Doubling the number of turns cuts force by 16×, which is why designers pick the fewest turns that still give the needed travel.

Design gotchas:

• Wave springs need a bore or shaft to ride on — they don't self-center. Radial clearance is typically 1–2% of diameter.
• Waves must nest correctly in multi-turn types; installing one flipped kills the load rating.
• Deflection should stay below ~80% of free-height-minus-solid to avoid taking a permanent set.
• They handle static and low-cycle loads well but fatigue faster than coil springs at high cycle counts — check the S-N curve if you're above 10⁶ cycles.

Concrete example: A NEMA 23 servo motor uses a single-turn wave spring under the rear bearing outer race. It provides ~30 N of preload in a 2 mm axial space — a coil spring giving the same force would need ~10 mm, forcing a longer, heavier motor.