The humble screw dates back to the Pythagorean philosopher Archytas of Tarentum in the 5th century B.C., and design innovations over the centuries have been rare. But every once in a while a maverick like Leon Simons comes along to shake up the Establishment.
Simons, a 78-year-old inventor and MIT graduate, recently received a U.S. patent for a revolutionary wood screw that will not loosen its grip despite vibrations; indeed, the screw tightens over time.
"A screw is a screw, right?" asked Simons. "Wrong. You can certainly make improvements."
A veteran screw designer with more than 10 screw patents to his credit, Simons might be one of the world's few inventors to make a comfortable living off screw royalties: He earns six figures a year from Southern Fastening Systems, according to a company spokesman.
The North Carolina company has sold hundreds of millions of a Simon-designed screw annually since the early '70s. More recently, Simons licensed four screw patents--including one for a new "Simons Head" screw that resists stripping--to an English manufacturer.
"My screws are everywhere. My screws have gone to the moon" in NASA equipment, the inventor said.
While sitting at a dining room table in his New York apartment recently, Simons explained the "trick" of his new wood screw and its advantage over competitors.
A conventional wood screw, he said, features a continuous thread that spirals around a cylindrical shank. When driven into the wood, it is held in place by friction.
But conventional wood screws often loosen because vibrations cause them to rotate out of their holes. Some users employ glue or try to swell the wood with water to tighten a wood screw, "but they still come out," Simons said.
The new wood screw solves the vibration problem in an unusual way. Because the notched threads on the shank are arranged in three twisting paths--what Simons calls a trilobular configuration--the screw tends to contract slightly (about 10 percent) as it is driven into wood. This physical action, the inventor said, resembles a braided rope that shortens as it is twisted into a hole.
As Simons' wood screw is driven into the wood, the threads, too, move closer together. Because the early impressions in the wood made by the threads do not match the final alignment of the threads, the screw is locked. It cannot be shaken loose because its re-formed threads are out of phase with the cuts in the wood.
"The more you shake it, the tighter it gets," the inventor said.
Simons said it took him a year to fine-tune his wood screw design. "Wherever I am, I work. It's the idea that counts. I don't need a lab to make a sketch."
Besides his work in fasteners, Simons said he holds more than 30 non-screw patents.
Reaction to Simons' wood screw is uniformly positive.
"It's a breakthrough," commented Tom Dreher, editor of Fastener Technology International, a trade journal.
"This is truly different," said John Huband, chief executive of European Industrial Services, a Birmingham, England-based screw manufacturer and the product's licensee. "Screws are the most deadly boring things on Earth. (But) the sales potential here is beyond belief--25 to 30 million pieces per year in the United Kingdom alone."
Huband expects furniture makers to be a large market for Simons' screw, as well as some automobile companies and container manufacturers. He said he might enter the $300-million U.S. wood screw market down the road, after conquering France and West Germany.
For his part, Simons says he will continue inventing, even though the work "is very difficult. You live with it night and day."