HENRY F. PHILLIPS, of Portland, Oregon, patented a new kind of screw and screwdriver in 1936. Within a decade his screws were holding things together all over the world. Why? Wasn’t one kind enough? For the average person tackling a minor do-it-yourself project, the advantages of the Phillips can seem elusive. Perhaps it was a scheme by the tool industry to make people buy twice as many screwdrivers.

But the ordinary screw and screwdriver are far from perfect, and the spread of assembly lines and mass production highlighted their deficiencies. To seat the business end of a screwdriver into a slot screw, you have to make sure the blade and slot line up exactly. That takes only a moment, but in high-volume manufacturing those moments add up. The slot design is particularly ill-suited for use with power tools. Unless the screwdriver is centered with absolute precision, the blade tends to go flying out.

Screws that replace the slot with a socket, such as the cavity that fits an Allen wrench, offer a snugger fit. But punching deep sockets into screw heads tends to deform or damage them, so slot screws were always far easier and cheaper to manufacture. Then, in 1907, a Canadian named Peter L. Robertson patented a square-socket screw that could be efficiently massproduced, and a number of Canadian factories adopted it. But he failed at marketing his design beyond Canada, apparently because of both the disruption of World War I and his insistence on retaining complete control over his technology.

Phillips’s five 1936 patents describe a fastening system involving a shallow cruciform recess and a matching driver with a tapering tip. His first application, filed in 1934, envisioned a screwdriver that ended in a sharp point. A second application, filed a year later by Phillips and Thomas M. Fitzpatrick, of Portland, described the blunt-ended design that remains in use today. Like Robertson’s square-socket design, the Phillips system is self-centering: Press the tip against the socket, and a little wiggling will seat it properly.

Phillips founded the Phillips Screw Company to license his patents. After three years of rejection, he finally persuaded the American Screw Company to manufacture the screws. Engineers there balked until the president of the company threatened to fire anyone who said it couldn’t be done. American Screw then spent $500,000 developing a manufacturing process and induced General Motors to use the screws on its 1936 Cadillac. By 1940 virtually every American automaker had switched to Phillips screws.

The conveniently selfcentering driver turned out to be conveniently self-ejecting as well. The combination of a shallow socket and a tapered blade made the driver pop out of the socket whenever it encountered a lot of resistance, a phenomenon known as “camout” or “torque-out.” This, the most vexing shortcoming of the Phillips system for casual users, proved to be an advantage for automakers and other manufacturers, cutting down on overscrewing.

During World War II, tanks, jeeps, and aircraft held together by Phillipshead screws began rolling off assembly lines. The screws boosted industrial productivity, but, for the weekend handyman, they only created problems. Cam-out makes tightly driven Phillips screws fiendishly hard to remove and often damages the screw, the driver, and anything a suddenly loose driver happens to hit. Whereas a dime or a piece of scrap metal can often be used to loosen a slot screw, nothing takes the place of a Phillips screwdriver. A flat-bladed driver or even a wrong-size Phillips one just makes cam-out worse.

Phillips himself died in semiobscurity in 1958 at the age of 68, long after his invention had become a household name. The Phillips Screw Company, now based in Wakefield, Massachusetts, continues to research and license fastener technology. The company has developed a number of improvements to the basic Phillips design. Its ACR Phillips II employs interlocking ribs in the driver and socket to eliminate cam-out; its Pozidriv system uses flanges between the driver blades, and matching grooves in the socket, to reduce wear and allow firmer engagement.

The Robertson squaresocket screw is still popular in Canada and is used by a number of U.S. furniture and mobile-home manufacturers. Other socket designs in common use include the hexagonal Alien socket and the star-shaped Torx. The Phillips, however, remains the international socket screw of choice. Once a standard is in place, it can be as difficult to dislodge as a tightly driven Phillips screw.