Why is it that anytime I need to turn a slot-head screw, my tool drawer contains five or six Phillips-head drivers but not one flat-blade screwdriver? Maybe a better question is, why does the world need more than one type of screwhead? After all, the U.S. railroad industry managed to stick with a universal standard (all train cars run on the same 4-ft.-8-1/2-in.-spaced rails), and we enjoy the convenience of a standard fit for electrical outlets and plugs. Without such universality, life would be, well, screwy.
To compound the design disparities among screwheads, we must also contend with hex-head, square-drive (Robertson), panhead, star-shaped (Torx) and even headless setscrews. Some people have speculated that tool designers created new styles of screws because they became tired of the basic flathead. Others think it was a conspiracy by manufacturers to force consumers to buy more drivers. However, in this case neither fashion nor profit drove innovation.
The first metal screws used as fasteners date back to the 15th century. They had square or hexagonal heads and were turned with a wrench, not a screwdriver. At the end of the 1700s, screw-cutting lathes were developed, making screws more widely available and consistently sized.
By the early 1800s, slot-head screws and their companion flat-blade screwdrivers became woodworkers' fastening tools of choice. The original flat-blade screwdrivers (inspired by the bits of carpenter's braces) were flat along their entire length. But because a round rod offered greater strength, toolmakers eventually made screwdrivers from heavy wire and flattened only the tips.
Slot-head screws were essentially the only players until 1908, when the Robertson (square-drive) screw was introduced by Canadian salesman-turned-inventor P.L. Robertson. Motivated by a painful mishap with a flat-blade screwdriver, Robertson created the new socket-head design to prevent screwdrivers from slipping off of the screws. The Robertson screw's self-centering feature made it easy to seat and ideal for production lines, leading the Fisher Body Co. to use the Robertson screw for assembling bodies for the Ford Model T and Model A. Still the most popular screwhead style in Canada, the square-drive screw predated the familiar Phillips design by about 25 years (surprise!).
In the early 1930s Henry Phillips of Portland, Oregon, patented the now famous cruciform-head screw. Like the Robertson screw, this fastener also self-centered but tended to cam-out — and sometimes “strip” — when tightened. Ironically, that pesky characteristic made the Phillips screw ideal for power drivers used on production lines because itprevented over-tightening. In 1937 General Motors began using Phillips-head screws for assembling its Cadillac models, initiating Phillips as an international name. Since then, many modifications and variations have followed Phillips' and Robertson's designs — behooving DIYers everywhere to own (and organize) a plethora of screwdrivers.