Spanner in the works

To put or throw a spanner in the works is to cause a disturbance, just as a spanner would if it were thrown deliberately into the workings of machinery. Perhaps this was actually done by some disgruntled worker in the past but the first date of the figurative expression is the subject of some debate. Some sources say that it was first used figuratively in the 1930s; others say it was earlier from the late 19th/early 20th century. The American equivalent is a monkey wrench in the works.