# Differential screw (fine adjustment)

> How does a differential screw give fine adjustment?

- Category: Mechanisms › Screws
- Kind: Hardware
- Basis: Xem Studio drawing; classic mechanism (Brown No. 266)
- Page: https://xemstudio.com/objects/differential-screw-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=differential-screw-mechanism · Plain text: https://xemstudio.com/objects/differential-screw-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Two threads of pitch p₁ and p₂ on one screw, each in its own nut, one nut fixed: a turn moves the free nut by p₁ − p₂ (0.25 mm for 1.25 and 1.0 mm), with the strength of coarse threads.
- Same hand on both threads gives the difference; opposite hands give the sum (a turnbuckle).
- Used in micrometer stages and precision adjusters. Brown's movement 266 shows a shaft with two pitches moving a bearing by their difference.
- Parts (each has its own page): differential-screw-m8, threaded-rods-metric, hex-nuts-metric. Brown's movement No. 266 shows it (1868).

## Sizes

| parameter | value |
|---|---|
| pitch p₁ | 1.25 mm |
| pitch p₂ | 1.0 mm |
| advance / turn | 0.25 mm |

## Where the files are

- Henry T. Brown (1868, public domain): [Five Hundred and Seven Mechanical Movements — scan on archive.org](https://archive.org/details/fivehundredseven00browiala) — web — Publisher's page; dimensions are facts

## Questions

**How does a differential screw give fine adjustment?**

Two threads of pitch p₁ and p₂ on one screw, each in its own nut, one nut fixed: a turn moves the free nut by p₁ − p₂ (0.25 mm for 1.25 and 1.0 mm), with the strength of coarse threads.

## Fits with

- [Differential screw, M8×1.25 / M8×1 (concept rod)](https://xemstudio.com/objects/differential-screw-m8/)
- [Threaded rod, metric: M4 × 194.2](https://xemstudio.com/objects/threaded-rods-metric/)
- [Hex nuts, M2–M8 (ISO 4032)](https://xemstudio.com/objects/hex-nuts-metric/)