# Torsion spring wire Ø0.8, OD 8, 6 coils

> What are the dimensions of a small torsion spring?

- Category: Hardware › Motion
- Kind: Hardware
- Basis: Close-wound helical torsion spring with two straight tangential legs; rate E d⁴ / (3667 D n) N·mm per degree
- Page: https://xemstudio.com/objects/torsion-spring/ · JSON: https://xemstudio.com/api/geometry?object=torsion-spring · Plain text: https://xemstudio.com/objects/torsion-spring/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- Six close-wound coils of 0.8 wire, OD 8, ID 6.4, with two straight legs reaching 10 mm from the coil axis. Envelope 14 × 8 × 5.7.
- Torsion rate in N·mm per degree = E d⁴ / (3667 D n), E the wire's elastic modulus, D the mean Ø (7.2), n the coils.
- The ID (6.4) goes over an arbor; the legs bear on the two parts it sets against each other, such as a pawl and its frame.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| spring OD | OD (6–16) | pocket of the same Ø | socket | all |
| spring ID | OD − 2 × wire | guide rod or arbor of the same Ø | socket | all |

## Sizes

| feature | value_mm |
|---|---|
| wire Ø | 0.8 |
| OD / ID | 8 / 6.4 |
| coils | 6 |
| leg reach from axis | 10 |
| envelope | 14 × 8 × 5.7 |

## Where the files are

- Wikipedia: [Spring (device)](https://en.wikipedia.org/wiki/Spring_(device)) — web — CC BY-SA 4.0 (text)
- McMaster-Carr: [Compression springs (free STEP per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/compression-springs/) — STEP, PDF — McMaster-Carr site terms (verify at link)
- Lee Spring: [Spring design formulas](https://www.leespring.com/learn-about-springs) — web — Lee Spring site (verify at link)
- Long Earth Society: [Engine and rig builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/torsion-spring/index.json

- torsion-d0.8-od8-l10: [STEP](https://xemstudio.com/files/hardware/springs/torsion-d0.8-od8-l10.step) · [STL](https://xemstudio.com/files/hardware/springs/torsion-d0.8-od8-l10.stl) — torsion spring envelope: wire Ø0.8, OD 8, ID 6.4, legs reaching 10 mm from the axis, 6 coils

## How it fits

### Connects to
- [Pawl 24 mm with a Ø3 pivot for the Ø40 ratchet wheels](https://xemstudio.com/objects/ratchet-pawl/): holds the pawl on the teeth

### Alternatives
- [Compression springs, wire Ø0.5–1.6, OD 6–16](https://xemstudio.com/objects/compression-springs/): linear return

## Questions

**How do I calculate a torsion spring rate?**

N·mm per degree = E·d⁴ / (3667·D·n), with D the mean coil Ø and n the coils.

**What arbor fits the torsion spring?**

The coil ID is 6.4.

## Fits with

- [Pawl 24 mm with a Ø3 pivot for the Ø40 ratchet wheels](https://xemstudio.com/objects/ratchet-pawl/)
- [Compression springs, wire Ø0.5–1.6, OD 6–16](https://xemstudio.com/objects/compression-springs/)
- [Extension springs, wire Ø0.6 and Ø1.0](https://xemstudio.com/objects/extension-springs/)