Robertson screwdriver
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| Screw drive types | |
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Slotted (flat or straight) |
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Phillips ("crosshead") PH |
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Pozidriv (SupaDriv) PZ |
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Square |
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Robertson (square) |
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Hex |
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Hex socket (Allen) |
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Torx T, TS, TX |
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Tri-Wing |
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Torq-set |
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Spanner head (Snake-eye) |
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Triple square XZN |
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Polydrive |
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One-way - Clutch |
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Spline drive |
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Double hex |
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Bristol |
A Robertson screwdriver (also called a square drive screwdriver) is a type of screwdriver with a square-shaped tip with a slight taper (in the same way that flatheads, Phillips, hex, and Torx have flat, x-shaped, hexagonal, and hexagrammal tips, respectively). Robertson screws are used mainly in Canada (where they are very common), though they can be found elsewhere.[1]
Canadian P.L. Robertson invented the Robertson screw and screwdriver in 1908. He received a patent in 1909, and later applied for and received other patents. The last patent expired in 1964.
Robertson screwdrivers are easy to use one-handed, since the tapered socket retains the screw, even if it is shaken.[2] They also allow for the use of angled screw drivers and trim head screws. The socket-headed Robertson screws are self-centring, reduce cam-out, stop a power tool when set, and can be removed even if painted-over or old and rusty.[3] In industry, they speed up production and reduce product damage.[4]
- US Patent 6729 Cummings 1875[dead link] Link to United States patent for square headed screw type that pre-dates Robertson's patent. This prior art should have rendered Robertson's patent claims invalid.
Robertson had licensed the screw in England, but the party with which he was dealing intentionally drove the company into bankruptcy and purchased the rights from the trustee, thus circumventing Robertson.[citation needed] He spent a small fortune buying back the rights. Subsequently, he refused to allow anyone to make the screws under licence. When Henry Ford tried out the Robertson screws he found they saved considerable time in car production, but when Robertson refused to license the screws to Ford, he realized that the supply of screws would not be guaranteed and stopped using them.[5][6][7]
[edit] Recess dimensions
Robertson-head screwdrivers are available in range of tip-sizes. A given driver's suitability for use with a particular size of screw and recess size is indicated upon its handle according to the following colour code:
| Colour | Screw types | Fraction | Range |
|---|---|---|---|
| Orange (#00) | No. 1 & 2 | 1/16 in.+ | 1.77–1.80 mm (0.070–0.071 in) |
| Yellow (#0) | No. 3 & 4 | 3/32 in.- | 2.29–2.31 mm (0.090–0.091 in) |
| Green (#1) | No. 5, 6 & 7 | 7/64 in.+ | 2.82–2.86 mm (0.111–0.113 in) |
| Red (#2) | No. 8, 9 & 10 | 1/8 in.+ | 3.34–3.38 mm (0.131–0.133 in) |
| Black (#3) | No. 12 and larger | 3/16 in.+ | 4.81–4.85 mm (0.189–0.191 in) |
[edit] Footnotes
“A Study in Evolution”
- ^ Rybczynski 2000, p 85.
- ^ Rybczynski 2000, p 86.
- ^ Rybczynski 2000, pp 82, 86.
- ^ Rybczynski 2000, p 82.
- ^ "Robertson Screws". http://www.mysteriesofcanada.com/Ontario/robertson_screws.htm.
- ^ "History of Screws and Screwdrivers". http://inventors.about.com/od/sstartinventions/a/screwdriver.htm.
- ^ "Caledonia: Along the Grand River". http://books.google.com/books?id=sCZuETU7u5oC&pg=PA58&lpg=PA58&dq=ford+robertson+screw&source=web&ots=G6rG-rlis3&sig=nDpc5ijkfNi8lvSPcaMXsLo8hb0#PPA58,M1.
[edit] References
- Rybczynski, Witold (2000). One Good Turn: A Natural History of the Screwdriver and the Screw. Toronto, Ont., Canada: Harper Flamingo. ISBN 0-00-200031-8.
[edit] External links
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Wikimedia Commons has media related to: Robertson screw |
- Robertson Inc. official web site
- US Patent 6729 Cummings 1875[dead link] Link to United States patent for square headed screw type that pre-dates Robertson's patent. This prior art should have rendered Robertson's patent claims invalid.
- Robertson screw on Canadian Broadcasting Corporation's 50 Greatest Canadian Inventions list
