Complex sentence: Hutton made compasses that were hidden inside pens or tunic buttons, he used left-hand threads so that, if the Germans discovered them and the searcher tried to screw them open, they would just tighten.
Split into simpler sentences: Hutton made compasses that were hidden inside pens or tunic buttons. He used left-hand threads so that, if the Germans discovered them and the searcher tried to screw them open, they would just tighten.