The Allen wrench is one of those things that is so ubiquitous you’re apt to take it for granted. 

I’ve got a bunch of these L-shaped pieces of metal distributed all over my house. There’s an Allen wrench on top of my dresser. There’s one in my bathroom cabinet. There are a few stashed in my office desk. And my junk drawer runneth over with them.

For some reason, the Allen wrench sitting on my bedroom dresser grabbed my attention this morning and got me wondering, “What’s this thing’s story? Why do I have so many of these wrenches lying around? Why is it so satisfying to fasten screws with one?” 

So I started investigating. 

Here’s what I learned about this omnipresent, incredibly-handy-but-typically-underrated tool. 

The History of the Allen Wrench (aka the Hex Key)

Screws have been around for thousands of years, but it wasn’t until the industrialization of the 19th century that they became a standard fastener. The first screws had a slot head/flathead, and you would use a flathead screwdriver to drive the screw into wood. The downside of slotted screws is that the screwdriver tends to slip out of the slot, especially as you apply more torque, leaving you with a stripped screw.

Seeing this issue, innovative Americans between the 1860s and 1890s started to design screws that had square- or triangular-shaped sockets. Instead of only having a single contact surface between the socket and the screwdriver, square or triangular sockets gave you three or four contact surfaces. More contact surfaces = reduced chances of driver slippage.

While the patents for screwheads with square or triangular sockets were filed in the 19th century, it wasn’t until 1908 that the first commercialized square socket hit the market. They didn’t attract much attention. 

Then sometime between 1909 and 1910, an American named William G. Allen patented a screwhead with a six-sided hexagonal shape and accompanying hexagonal driver, called a hex socket key. His company, the Allen Manufacturing Company of Hartford, Connecticut, began marketing this new screw as the “Allen Safety Screw.”

In 1911, another outfit — the Standard Pressed Steel Company — created their own version of the hex socket screw and accompanying hexagonal driver. According to the company’s telling of events, their creation of the hexagonal socket and driver was simultaneous with and independent of the invention of the Allen Safety Screw. Other inventors in other countries appear to have independently invented versions of the hex head screw and driver around the same time as well. It must have been an idea whose time had come. 

Likely driving the push towards the hex head was the industrial safety campaigns of the Progressive movement. The hex head was seen as a safer alternative to traditional slot head screws since they minimized the slipping of drivers. Also, the design allowed for the creation of headless or recessed screws, which reduced the chances of a worker’s clothing catching a screw head and getting pulled into the line shafting that was commonly used in early 20th century factories. 

Despite the benefits of the hex head screw, it was slow to take off. It wasn’t until World War II and America’s creation of the “arsenal of democracy” that they came into widespread use. 

After the war, hex head

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