Screw This, Screw That: Why We Have Different Types of Screws

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If you've ever mistakenly grabbed the Phillips head screwdriver when you needed a flat head, you've probably asked yourself why there are different types of screws. Let's start at the beginning.

The screwdriver, originally called a screwturner or turnscrew, entered the world inconspicuously and kept a very low profile until its 300th birthday. Historians believe it was invented in Germany, but aren't sure exactly when. The Medieval Housebook of Wolfegg Castle, the oldest known written reference to the tool, has a hazy publishing date somewhere between 1475 and 1490. Considering the invention likely predates the book by at least a few years, the mid to late 15th century is about as exact a birthday as it gets. For about 300 years, the persistent presence of screws is the only solid evidence that screwdrivers even existed. Then, suddenly, documentation of screwdrivers exploded across Europe, particularly in France.

Early screwdrivers had pear-shaped handles and were made for slotted screws. Metal screws as we know them today have been in use since at least the 15th century for cabinetry work and to secure plates on jousting armor. Before that, wooden screws were used in wine and olive oil presses as far back as the 1st - 3rd century BC (how they turned them for so long without a screwdriver, I haven’t been able to figure out).

These early metal screws were prohibitively expensive. It wasn’t until several advances in screw making – among them, Jesse Ramsden and Henry Maudslay's screw-cutting lathes and David Wilkinson’s and Job and William Wyatt’s mass production of screws on assembly line-like systems – occurred around the beginning of the First Industrial Revolution that the screw became easy enough to produce to become popular and widespread. This increase in popularity, of course, led to the refinement and diversification of the screwdriver. The tool took on many different shapes and sizes, though for a long time every version was still for flat slotted screws, which were the only type around.

Better Heads

This changed in 1908, when Canadian P.L. Robertson patented the “first recess-drive type fastener practical for production usage,” a recessed square-drive screw that bears his name. Robertson screws became a standard in Canada and gained a buzz in the U.S. when the Ford Motor Company, one of Robertson's first customers, used over seven hundred of them on each Model T. The square-drive head on Robertson screws had an advantage over slot heads because the driver was relatively easy to get situated on the head and stayed put during installation once it was there. A screw like Robertson’s became crucial as American manufacturers moved increasingly toward mass production methods. The time it took to align the driver with the slot, multiplied across thousands of workers in a factory and across hundreds, if not thousands, of screws per worker per day, became a significant loss of time and money. Additionally, the automated screwdrivers used on assembly lines often slipped out of the screws’ slots and into whatever component was being assembled or stripped the screw once it was driven all the way. [Image credit: Saforrest]

The American automobile industry was especially in need of a screws screw that could stand up to the torque of their automated drivers and be fitted and tightened quickly, but a bad break in Robertson’s past doomed him just when his invention was needed most. Dealing with dishonest parties while licensing his screw in England, Robertson wound up losing the rights to his invention and had to spend a small fortune to buy them back. When Ford, wanting to protect his assembly advantage (the screws saved his workers two hours of assembly time per vehicle), asked for a licensing agreement from Robertson so that he could manufacture and control the distribution of the screws, Robertson turned him down and he refused to allow anyone to make the screws under license. After their run on the Model T, Ford had to limit the use of the screws to his Canadian division and the widespread adoption of the Robertson screw in the U.S. fizzled and failed.

Enter Portland, Oregon-based businessman Henry F. Phillips and the patent for a screw with a deep X-shaped slot, which he had purchased from friend and inventor J.P. Thompson. Phillips refined the design of the fastener, today known as a Phillips screw, for automated screwdrivers. The X-shape of the slot and pointed tip of the Phillips head screwdriver made the driver self-centering and unlikely to slip out when it wasn’t supposed to. The recessed slot was shallow enough, though, that the driver did pop out when the screw was fully tightened, which prevented over-torquing and damage to the screw, the driver and the product being assembled.

The American Screw Company began mass-producing Phillips’ design. A successful trial on the 1936 Cadillac helped it proliferate through the U.S. auto industry. By 1940, 85% of the screw manufacturing companies in the U.S. had a license to produce the Phillips screw design. Usage spread from the auto manufacturers as the Phillips drive system was used during the Second World War on many wartime products and vehicles. Though originally meant for automated, industrial applications, Phillips screws and handheld screwdrivers found their way into the toolboxes of handy men and women across the country by the turn middle of the century. [Image credit: U.S Patent and Trademark Office.]

Other Ways the World Turns

Most anyone who’s had to fix anything at home or put together an IKEA couch has heard of slotted and Phillips screws and maybe even hex sockets. The world of screws is vast, though, and plenty of other types of screw heads and drives exist, like the Mortorq, the Pozidriv and the Bristol. You can take a crash course in the different types of screws here, and if you want a more in-depth history of screws and drivers, check out Witold Rybczynski’s One Good Turn: A Natural History of the Screwdriver and the Screw.

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January 21, 2011 - 8:54am
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