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The Robertson 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. But slotted screws and their associated drivers were easy to make. 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. The internal square drive required a bit more manufacturing ingenuity than did making the cheap yet popular slotted head, however.

Robertson Drive History

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 rotate the driver 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. The idea had been patented by another inventor in the latter part of the 19th century but it remained more of a curiosity as manufacturing techniques of the time lacked the ability to produce a commercial form. Manufacturers took to Robertson’s designs right away, and companies, such as Ford, came to depend on the screws and driver as key components in automobile production as it saved assembly time. As a result, Robertson soon produced special metal screws for Ford’s use in automobile manufacturing. Henry Ford sought a licensing arrangement with Robertson, but Robertson turned him down. Ford was concerned about maintaining availability of the fasteners, and without licensing, he limited the use of the Robertson design to cars that he built in Canada.

Another development was underway in the screw head world, one that took a while to catch on but by World War II had nearly 40 licensees worldwide. Henry Phillips had shown his new cruciform socket design to many major screw manufacturers but it was not until he showed it to Eugene Green in 1933 that it caught the interest of the American Screw Co.’s newly appointed president. The Phillips screw began showing up in Cadillacs shortly thereafter and became prolific after the cold forming method of making the cruciform socket was perfected.

An advantage of the Phillips head over the Robertson design was that it could “cam out” after reaching a certain torque level, preventing damage to the screw and driver from over-torquing. This was at a time when torque-controllable screwdrivers had not yet arrived.

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 thrives there today, Robertson screws and screwdrivers were much less successful in the US and are not commonly used. With the growth of screw use in the construction industry and the availability of portable, powered drivers, the Robertson design is seen more and more on this side of the border, particularly for deck installations and the like. The slight taper of the socket and drive allows for a “cling” fit, an especially useful feature when driving lots and lots of screws vertically from above. The original patent expired in 1964 which too may account for the form showing up more frequently in the States.

On the industrial side of things, square-headed bolts became obsolete with the advent of hex bolts and a similar situation developed with the hexagonal socket. The shallower drive angles of the hexes made for better torque transfer and the development of ball-nosed hex keys made it possible to drive the hex sockets at an angle, another benefit of the Phillips design. Cam-out became a less desirable feature with torque-controlled drivers increasingly available. But it was another necessity that led to the development of the Allen hex socket – about the same time as the Robertson drive: the need to remove the hazard of exposed set screws which, installed to hold transmission components on rotating shafting, presented a snagging hazard.

Development of fastener heads since then has followed many paths with improved resistance to cam-out, shallower drive angles for better torque capacity, better capability for automated assembly, and so on. Torx® and Pozidriv® heads are well known in automotive and aerospace industries and have made their way into other industries as well. A lively, technical discussion on the trials and tribulations of removing various screw heads may be found here.

Robertson Screwdriver Types

Currently, there are five different Robertson screwdriver types 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.

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.

drivers (#0) work with screw types 3 and 4 and feature a recess size range of 2.29 to 2.31 mm. Green Robertson screwdriver (#1) operates with screw types 5, 6, and 7, with a recess size range of 2.82 to 2.86 mm.

Robertson screwdriver (#1) operates with screw types 5, 6, and 7, with a recess size range of 2.82 to 2.86 mm. Red Robertson screwdriver functions with screw types 8, 9, and 10 and has a recess size range of 3.34 to 3.38 mm.

Robertson screwdriver functions with screw types 8, 9, and 10 and has a recess size range of 3.34 to 3.38 mm. Black Robertson drivers work with the largest screws, types 12 and higher, and have a recess range of 4.81 to 4.85 mm.

Where to buy

Robertson, Inc. remains in business to this day and continues to produce a range of fastener products and drives for furniture makers, deck builders, sheet metal fabricators, etc. With the expiration of the patent, knock-off versions have become ubiquitous and are available in major home supply stores and are as easily sourced online. The company also has several combination heads that incorporate, for instance, both the Robertson and the Phillips designs.

Summary

This article presented a brief discussion of the Robertson drive. For more information on other products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources.

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