Robertson screwdriver
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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, ×-shaped, hexagonal, and hexagrammal tips, respectively). Robertson screws are used mainly in Canada, though they can be found elsewhere.
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 (i.e., without using the second hand to hold the screw), in fact, when driving a screw one handed, the user can let go of the driver, and the driver will stay put in the screw. They also allow for the use of angled screw drivers and trim head screws.
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. After that, he refused to ever allow anyone to make the screws under license. When Henry Ford tried out the Robertson screws he found they saved considerable time in the production of cars but when Robertson refused to license the screws to Ford, he realized that the use of the screws would not be guaranteed and stopped using them.[1][2][3]
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:
| Color | Screw types | Max | Min | Fraction |
|---|---|---|---|---|
| Orange (#00) | No. 1 & 2 | 0.0710 in. | 0.0696 in. | 1/16+ |
| Yellow (#0) | No. 3 & 4 | 0.0910 in. | 0.090 in. | 3/32- |
| Green (#1) | No. 5, 6 & 7 | 0.1126 in. | 0.111 in. | 7/64+ |
| Red (#2) | No. 8, 9 & 10 | 0.1330 in. | 0.1315 in. | 1/8+ |
| Black (#3) | No. 12 and larger | 0.191 in. | 0.1895 in. | 3/16+ |
Footnotes
References
- Rybczynski, Witold (2000). One Good Turn: A Natural History of the Screwdriver and the Screw. Toronto, ON, Canada: Harper Flamingo. ISBN 0-002-00031-8.