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Differential screw (fine adjustment)
How does a differential screw give fine adjustment? · Hardware · basis: Xem Studio drawing; classic mechanism (Brown No. 266)
Also called: differential screw, differential thread, fine adjustment screw, tornillo diferencial, parafuso diferencial, Differentialschraube, vis différentielle
Exact dimensions. True size, with no printing tolerance added.
- sizes
- 3 in table
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).
Differential screw size chart
| parameter | value |
|---|---|
| pitch p₁ | 1.25 mm |
| pitch p₂ | 1.0 mm |
| advance / turn | 0.25 mm |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Henry T. Brown (1868, public domain) | Five Hundred and Seven Mechanical Movements — scan on archive.org | web | Publisher's page; dimensions are facts |
Xem scan
Not needed Published standard; the sheet is the geometry.
https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.Plain text: sheet.txt · JSON: /api/geometry?object=differential-screw-mechanism
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.