wrench

put/throw a spanner in the works (British & Australian, American)

to do something that prevents a plan or activity from succeeding. We were hoping to get the project started in June but the funding was withdrawn so that rather threw a spanner in the works. The sudden withdrawal of the guest speaker really threw a monkey wrench in the works.

See also: throw, work

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throw a monkey wrench into something

to cause something to fail. We keep trying to get together, but her crazy schedule keeps throwing a monkey wrench into our plans.

See also: monkey, throw