put a spanner in the works

The phrase "put a spanner in the works" is an idiomatic expression that means to disrupt or hinder a process or cause complications that prevent something from progressing smoothly. It implies causing a setback or obstacle that delays or derails the intended outcome or plan. The term "spanner" refers to a wrench, and "works" refers to a machinery or system, indicating that something is being thrown into the functioning mechanism to cause trouble or dysfunction.