The Roberston screwdriver, also known as a square screwdriver, was invented in 1908 by P.L. Robertson, a native Canadian. The screwdriver presented a solution to the frequent problem users encountered with flathead screwdrivers: the driver often slipped out of place and slowed down the process of securing the fasteners. Robertson’s design depended on the corresponding square shape on the top of screws that enabled the square-shaped screwdriver to make secure contact with the screw. As the screwdriver was rotated, it was far less likely to slip out of place and the process moved a lot faster.
Once Robertson had conceived the notion of a square-headed screwdriver, he toyed with various manufacturing methods until he was able to produce screws with a square-shaped imprint on their heads. When the correctly-sized driver is inserted into a corresponding screw, the user can rortate the driver horizontally without fear of the driver slipping. Because the driver is self-centering, only one hand is needed for rotation.
Robertson patented his invention of both the square-headed screw and driver in 1909, but The Steel Company of Canada did not take kindly to his invention. Some went as far as to try to undermine his patents, but the attempts were unsuccessful. Manufacturers took to the new designs right away, and companies, such as Ford, came to depend on the screws and driver as key components in automobile production. As a result, Robertson soon produced special metal screws for Fords’ use in Model A manufacturing. Henry Ford sought a licensing arrangement with Roberston, but Robertson turned him down.
By the end of the late 1940s, Robertson’s company had grown to employ 500 people and the screws were available in three different sizes with corresponding drivers, each distinguished by one of three colors: small drivers were green, medium drivers were red, and large drivers were black. Although the design was rapidly integrated into the Canadian market and still continues to thrive today, Robertson screws and screwdrivers were much less successful in the US and are not commonly used.
Currently, there are five different Robertson screwdrivers available, with suitable screw size indicated by the color. Orange drivers (#00) are appropriate for use with screw types 1 and 2. The recess size range (the size of the corresponding square imprint on the screw) is from 1.77-1.80 mm. Yellow drivers (#0) work with screw types 3 and 4 and feature a recess size range of 2.29 to 2.31 mm. Green drivers (#1) operate with screw types 5, 6, and 7, with a recess size range of 2.82 to 2.86 mm. Red drivers function with screw types 8, 9, and 10 and have a recess size range of 3.34 to 3.38 mm. Black drivers work with the largest screws, types 12 and higher, and have a recess range of 4.81 to 4.85 mm.