The term "monkey wrench" was originally used to insult the tool's African-American inventor Jack Johnson.
In mid-December 2015 a meme that claimed the term “monkey wrench” was first used as a derogatory term concerning its African-American inventor Jack Johnson, started circulating online:
While the central theme of this meme (that white people used the term “monkey wrench” as a racial slur to demean its inventor) is false, there is some truth behind it. Jack Johnson was the first African-American world heavyweight boxing champion and he did patent a wrench in 1922. Johnson’s patent, however, did not mark the invention of the first adjustable wrench, nor did it spawn the origin of the term “monkey wrench.” Johnson’s patent was merely an improvement on a previous design and had little bearing on the history of the tool, which can be traced back to the 1840s.
In February 2005, the Jim Crow Museum published a brief history of the wrench in an attempt to answer a question about Jack Johnson and his 1922 patent:
Did Jack Johnson invent the wrench?
Jack Johnson, the first Black heavyweight boxing champion, patented a wrench (U.S. patent #1,413,121) on April 18, 1922. His patent was not the first for a wrench. Solymon Merrick of Springfield, Massachusetts, patented the first wrench in 1835. Charles Moncky, a Baltimore mechanic, invented the monkey wrench around 1858. Moncky’s wrench was named using a purposeful misspelling of his name. On September 9, 1913, Robert Owen Jr, of Shawnee, Ohio, received a patent for the “Double Acting Wrench” (ratchet wrench), arguably the most important advancement in wrench technology. Daniel C. Stillson, a steamboat firefighter, received a patented on September 13, 1870 for an invention later known as the Stillson pipe wrench.
Jack Johnson, the inventor, represents little more than an interesting historical footnote. He owes his fame and infamy to his boxing exploits and his violation of social norms.
While the Jim Crow Museum stated that the monkey wrench was named after its inventor, Charles Moncky, not all historians agree. Herb Page, for instance, wrote in a 2002 article entitled “Reach for the Wrench” in the Fine Tool Journal that Moncky was neither responsible for the tool’s invention nor its name, and that the latter stemmed from the wrench’s appearance:
Of course, over the years, some speculation indicated that the original inventor, a man named Monk or Monck was responsible for the name. However, this has been refuted by diligent historical and patent research. New England industrial pioneers, Loring Coes and Laurin Trask, around the end of the 19th century related the more plausible account. They indicated that the term “monkey wrench” was already in use prior to Coes’ early patent (1841) and referred at that time to the earlier English type of adjustable wrench where you turned the handle to adjust the jaws.
I now provide some further evidence to back up Coes and Trask’s allegation, in that a wrench labeled “Monkey Wrench” was depicted in the English tool catalogue issued by Timmins & Sons, which hails from the early to mid-1840s. Also, I show a very early English wrench from my collection that I reckon to be from about the same or an even earlier era. This item, with its rounded head and “twist the tail” (handle) to adjust the mouth feature, could easily inspire the image of a monkey. I conclude that the name came along with these early wrenches when they were shipped to America. This particular wrench is marked “5. Johnson Sheffield” with an “S.J.” in a flag logo and exhibits the very fine detailed workmanship characteristic of early Sheffield tools.
In summation, while boxer Jack Johnson did patent a wrench in the 1920s, this was not the original monkey wrench. Furthermore, the tool was not named “monkey wrench” in an attempt to demean its inventor, as the term “monkey wrench” has been in use since at least the 1840s and most likely referred to the tool’s original “twist the tail” method of adjusting the jaws.