A spanner is a metal tool whose end fits round a nut so that you can turn it to loosen or tighten it.
PHRASE
从中捣乱;横加阻拦;搅局
If someone throws a spanner in the works, they prevent something happening smoothly in the way that it was planned, by causing a problem or difficulty.
例句
A bad result is sure to throw a spanner in the works.糟糕的成绩肯定会坏事的。