# Extension springs, wire Ø0.6 and Ø1.0

> What are the dimensions of a small extension spring with loop ends?

- Category: Hardware › Motion
- Kind: Hardware
- Basis: Close-wound helical extension spring with a loop at each end; length over the loops
- Page: https://xemstudio.com/objects/extension-springs/ · JSON: https://xemstudio.com/api/geometry?object=extension-springs · Plain text: https://xemstudio.com/objects/extension-springs/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

- Close-wound bodies (coils at 1.02 × wire pitch so the turns stay separate) with a full loop each end; the length is over the two loops.
- 0.6 wire × OD 6 (ID 4.8), 30 over the loops, 20 coils; 1.0 wire × OD 10 (ID 8), 50 over the loops, 25 coils.
- Rate follows the same k = G d⁴ / (8 D³ n) as a compression spring, plus an initial tension from close winding; the loop ID is OD − 2 × wire and takes a hook pin.

## 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 |
| loop ID | OD − 2 × wire | hook pin | designed | extension-* |

## Sizes

| file | wire Ø | OD | ID | length over loops | coils | index D/d |
|---|---|---|---|---|---|---|
| extension-d0.6-od6-l30 | 0.6 | 6 | 4.8 | 30 | 20 | 9.0 |
| extension-d1-od10-l50 | 1.0 | 10 | 8.0 | 50 | 25 | 9.0 |

## 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 (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/extension-springs/index.json

- extension-d0.6-od6-l30: [STEP](https://xemstudio.com/files/hardware/springs/extension-d0.6-od6-l30.step) · [STL](https://xemstudio.com/files/hardware/springs/extension-d0.6-od6-l30.stl) — extension spring envelope: wire Ø0.6, OD 6, ID 4.8, 30 mm over the loops, 20 coils
- extension-d1-od10-l50: [STEP](https://xemstudio.com/files/hardware/springs/extension-d1-od10-l50.step) · [STL](https://xemstudio.com/files/hardware/springs/extension-d1-od10-l50.stl) — extension spring envelope: wire Ø1.0, OD 10, ID 8, 50 mm over the loops, 25 coils

## How it fits

### Connects to
- [GT2 timing pulleys, 16T–60T (2 mm pitch)](https://xemstudio.com/objects/gt2-pulleys/): belt tensioner arm

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

## Questions

**How is an extension spring's length measured?**

Over the two loops: 30 and 50 mm on these files.

**What is the loop size?**

The loop ID is the coil ID: 4.8 on the 0.6 × 6, 8.0 on the 1.0 × 10.

## Fits with

- [Compression springs, wire Ø0.5–1.6, OD 6–16](https://xemstudio.com/objects/compression-springs/)
- [Torsion spring wire Ø0.8, OD 8, 6 coils](https://xemstudio.com/objects/torsion-spring/)
- [GT2 timing pulleys, 16T–60T (2 mm pitch)](https://xemstudio.com/objects/gt2-pulleys/)