When the New York Times asked Canadian author Witold Rybczynski to write about the Millennium's "best tool," he had some difficulty choosing. His entertaining book One Good Turn describes how he carefully examined his toolbox for candidates. Many worthy tools, such as the try square, level, chalk line, tape measure, handsaw, plane, chisel, etc., were invented by the Romans or the Egyptians and so predated the Millennium. It was his wife who put him to thinking about the one tool that she always kept handy, the screwdriver.

Rybczynski's quest for the origins of this most common tool did not prove easy. Some tools, such as the frame saw, had obvious origins since they were developed in a logical response to a particularly vexing problem. Others such as the carpenter's brace appeared mysteriously from some brilliant individual's creative imagination. While the screwdriver can hardly be called poetic inspiration, the screw itself is a different matter. The screw is a helix, a very complicated shape that appears in visible nature only in climbing vines and in some seashells.

The screw was probably invented by that singular genius Archimedes, who also gave us, among other things, the compound pulley, the windlass and the water screw, a device for lifting water that has at its heart an elegant helical screw. About 300 years later, in the first century AD, Hero of Alexandria invented the vertical press, which was used to press olives and grapes. But it was another 1400 years before some bright light realized that the helix that could press olives could also serve as a kind of threaded nail.

Rybczynski found the first evidence of screws dating from the 15th century, when they were used in watches, guns and armour but it was another 300 years before they became common. Individual hand-made screws were just too difficult to make and were of poor quality. The first industrial process for making screws was developed in England in the 1760s but it was Cullen Whipple of Providence, RI, who invented the automated method of cutting screws in 1842.

From the beginning the slotted head, driven by the flat-bladed driver, was the standard. But slotted screws have several drawbacks. They easily "cam out" (slip) causing frustration, delay and even injury, and you cannot start them with one hand. From 1860 to 1890 industrious inventors filed a flurry of patents for new heads, but all proved difficult to manufacture.

Peter L. Robertson was a salesman who spent his spare time conjuring inventions in his workshop.

The solution was found by a 27-year old Canadian, Peter L. Robertson. He was a pitchman for a Philadelphia tool company, a traveling salesman who sold goods at trade fairs and on street corners throughout eastern Canada. He spent his spare time in his workshop. He invented Robertson's 20th century wrench-brace, a combination brace, wrench, vise, rivet maker and screwdriver. He patented an improved corkscrew, new cuff links and even a better mousetrap. In 1907 he patented his socket-head screw.

Robertson later said that he got the idea for his socket head while demonstrating a spring-loaded driver to an audience in Montreal. The blade slipped and injured his hand. The secret of Robertson's invention is the exact shape of the recess, which is squared, with chamfered edges, tapering sides and a pyramidal bottom.

Robertson found financial backers, talked the town of Milton, Ontario, into giving him a tax-free loan and established his own screw factory. His screw head really was a big improvement. The driver fit snuggly into the head and never cammed out. Robertson tried in vain to set up shop in England or the United States. American backers came forward but they insisted on control, which Robertson would not grant them.

Meanwhile American Henry F. Phillips of Portland, Oregon, also a traveling salesman, patented his cruciform screw, which during World War II became the international standard. The Robertson is now widely used only in Canada even though an independent study by the magazine Consumer Reports declared it far superior to the Phillips, which is notorious for slippage and stripped sockets. While Rybczynski declared the screwdriver and screw the tool of the Millennium, perhaps Robertson was justified in calling his invention "the biggest little invention of the 20th century so far."