English Idiom – Throw a spanner in the works or Put a spanner in the works.

Meaning – To do something that prevents an activity or plan from happening or being successful. This expression is used when something or someone introduces a problem, obstacle or something unexpected. A spanner in the works will cause delays to the progress of something in some way. This problem may be a result of carelessness – or sabotage.

In American English an adjustable spanner is called a monkey-wrench. As a result you might hear American people use the similar idiom – throw a monkey wrench in the works.

To remember this phrase imagine what would happen if somebody threw a spanner into a moving engine or machine. The spanner would likely cause the gears or machine parts to smash or stop working in some way.

In British English a spanner may also refer to a stupid or foolish person. “You forgot your wallet again? You are a complete spanner!” This usage is mildly offensive.

A set of spanners
A set of spanners


When could you use this idiom?

  • When unexpected last-minute changes cause you problems.
  • If somebody makes changes to a plan  – and puts the whole plan at risk.
  • When somebody suddenly cannot make a prior engagement.
  • A business unsuccessfully tries to release a new product.


  • Bobby: “We were hoping to get married in January but now we can’t.”
  • Mike: “Why not?”
  • Bobby: “My future mother-in-law threw a spanner in the works! She’s going to Australia in January.”

In The News:

£70 million striker could be Manchester United’s new Zlatan Ibrahimovic but Arsenal may throw a spanner in the works


  • Is there an idiom like this in your country?

What is an idiom?

An idiom is a word or phrase that is not taken literally.  An idiom is an expression that cannot be understood from the meanings of its individual words, but has a separate meaning of its own.

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