A spanner in the works
/ə ˈspænə ɪn ðə wɜːks/informalUK
What does “A spanner in the works” mean?
A spanner in the works means a problem that disrupts a plan or stops progress
A cancelled train can put a spanner in your holiday plans. Someone can also throw a spanner in the works deliberately by blocking an agreement.
The noun phrase names the problem; “throw” and “put” describe causing it. The American wrench version has the same meaning.
When do people say it?
Use it for an unexpected obstacle or for deliberate interference. “Spanner” is British; US speakers usually say “wrench” or “monkey wrench”.
“The missing permit threw a spanner in the works just before opening day.”
Is it formal or informal?
Register: informal. It is most at home in everyday conversation rather than formal writing. Most common in UK.
Where does it come from?
Imagine a tool getting caught in moving machinery. It prevents the mechanism from working, just as a problem can interrupt a plan.
Origin confidence: Disputed; treat with caution
How do you say “A spanner in the works” in other languages?
Last updated 2026-10-01