What’s the Story Behind the 'Monkey Wrench'?

Familiar to plumbers and mechanics alike, the monkey wrench is a durable tool with cross-shaped jaws capable of loosening or tightening even the most stubborn fittings. It’s so sturdy, it might even double as a weapon—though we don't advise using it that way.

But why is a plumber’s tool named after a primate? What’s the origin of the monkey wrench’s peculiar name?

The Birth of the Monkey Wrench

The term 'monkey wrench' can actually refer to various types of wrenches. Historically, this wrench had smooth jaws running perpendicular to the handle and adjusted vertically; a pipe wrench is similar but with serrated jaws. A crescent wrench, on the other hand, has jaws that run parallel (or nearly parallel) to the handle and features a movable jaw adjustable horizontally. Sometimes, a crescent or pipe wrench is mistakenly called a monkey wrench, though that’s not technically correct. Typically, a monkey wrench refers to a tool with smooth, vertical, adjustable jaws running sideways to the handle (like the one shown at the top of this article).

The origin of the monkey wrench name is just as murky as the wrench itself. Like many tools, several inventors contributed to the development of the adjustable wrench. However, the name most frequently associated with the monkey wrench is that of Charles Moncky, a mechanic from Baltimore, who crafted the wrench around 1858. The story goes that Moncky introduced a wrench that soon adopted a version of his last name.

Another version of the story places the invention in Springfield, Massachusetts, in 1854 at the Bemis & Call toolmaking plant. According to a 1932 article in the town’s Morning Union newspaper: 'There was a typical, ingenious Yankee named Monck who worked there and conceived the idea of adding a movable jaw to the wrench... Around the shop, it became known as Monck’s wrench and, with a Darwinian twist, eventually morphed into the monkey wrench.'

But are either of these stories accurate? Some historians remain skeptical. For one, Charles Moncky is just one of several similarly named individuals who have been linked to the invention of the wrench over the years. A Charles Moncke from London was mentioned, along with Americans such as Monk, Monky, Moncay, Munkey, and other simian-inspired names—each seemingly trying to add significance to the slang term.

There’s also the issue of chronology. Some sources point to earlier references to a monkey wrench in England, predating Moncky’s supposed invention. The Oxford English Dictionary traces the term back to a tool catalog from around 1807, and a man in England was even noted in a 1826 police report for 'stealing a monkey wrench.'

The most convincing evidence might be found in Appleton’s Dictionary of Machines, Mechanics, Engine-Work and Engineering, a 1852 reference book that attributes a 'screw wrench' to 'S. Merrick' from Springfield, Massachusetts, in 1835. Coincidentally—or not—that same town is where 'Monck' is said to have created his wrench, around the same time. The screw wrench was similar to the monkey wrench, though the name itself dates back even further.

It’s possible these two stories are connected, and linking them might bring us closer to the truth. According to author Vince Staten, who penned the 1996 tool history book Did Monkeys Invent the Monkey Wrench?, another version of the story suggests a Springfield machinist named Solymon Merrick was attempting to perfect the tool with help from one of his factory workers, who was nicknamed 'monkey' for reasons unclear. Because the factory made various types of wrenches, workers reportedly referred to it as the 'monkey’s wrench.'

Here’s another intriguing theory: When the monkey wrench first appeared, it was introduced as a counterpart to a tool called a 'key wrench.' Some began referring to it as a 'non-key wrench,' which was eventually misheard or misinterpreted as 'monkey wrench.'

So, what can we conclude from this often-conflicting history? We know that Solymon Merrick designed a wrench, possibly with the help of a worker whose name or nickname resembled 'monkey,' in the mid-1800s. However, the term 'monkey wrench' was already in use in England at the time. Merrick may have thought his idea was original, but it could have been a case of simultaneous invention.

The Legend of the Monkey Wrench

In 2015, a meme spread across social media suggesting that early 20th-century boxer Jack Johnson (1878–1946) was the inventor of the monkey wrench. According to the meme, the wrench's name was a racial slur created 'to tarnish this great accomplishment.'

The story isn't accurate, though it blends some factual elements. Johnson, a Black heavyweight champion, encountered significant racial hostility throughout his career. After defeating white boxer James Jefferies in 1910, riots erupted across the country. Johnson later fled the United States to avoid a prison sentence related to an alleged violation of the Mann Act, which prohibited transporting women across state lines for immoral purposes. Johnson was traveling with his future wife, Lucille, who was white, which likely led to law enforcement targeting him unjustly.

Another aspect of truth is that Johnson did, in fact, co-create a pipe wrench, which he developed with fellow prisoners while incarcerated at Leavenworth Prison. The wrench was an improvement over existing designs, offering a better grip and easier disassembly. The patent application was approved in 1922. The men allegedly turned down a $20,000 offer for the patent and instead founded their own tooling company, J.A.J. Wrench Corporation.

However, the term 'monkey wrench' was not used as a slur against Johnson. As we've seen, the term existed long before Johnson's time.

Introducing the Monkey Wrench: A Disruption

It’s difficult to talk about monkey wrenches without mentioning the well-known idiom 'throwing a monkey wrench into the works.' This phrase is commonly used to describe an action that disrupts or upsets a plan or event that was otherwise proceeding smoothly.

The OED traces this version of the phrase back to 1907. There's also the phrase 'throwing a spanner into the works,' with 'spanner' being another term for a wrench commonly used in the UK.

According to idiom expert Gary Martin, the phrase 'throwing a monkey wrench (or spanner) into the works' likely originates from the disastrous consequences of dropping a wrench into a piston or gear in an industrial setting. This would halt all operations immediately. Martin suggests the 'spanner' version of the idiom could be traced to as early as 1828 in New Zealand.

Monkeys frequently appear in industrial or labor-related expressions. For instance, the term 'grease monkey,' used to describe someone who works on cars and is often covered in grease, first appeared in print in 1928. As for the connection between primates and labor or tools, it's unclear. Some monkeys have been observed using stone tools, typically to access food. However, none have been seen crafting anything remotely resembling a wrench—at least not yet.

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