【have a screw loose】 —(coll.) be mentally defective or not acting normally:

• I don’t go much with anarchists. It’s my judgment they nearly always 【have a screw loose】 .

【there is a screw loose】 —(coll.) there is smth. wrong in the condition of things:

• Now this may come into court, you know. If 【there is a screw loose】 anywhere, better mention it.

Note: Neither expression is antonymous in meaning to the phrase tighten up screws—

1. suppress or “clamp down” on dissenters, etc.:

• The president is using Russo-American rapprochement as a smokescreen for tightening up screws at home.

2. apply pressure; make smth. subject to more severe control:

• Dellinger believed the victory was a result of his team tightening up screws on defense.