Despite the apparent simplicity of a broken bolt on a safety harness, the plaintiff’s failure to present expert testimony in a products liability suit revolving around that part was grounds for dismissal, the U.S. Court of Appeals for the Third Circuit ruled.

In a decision that sheds light on what falls within jurors’ common knowledge, the appeals court upheld the dismissal of a suit by a man who said he was injured when a broken bolt caused his harness to fail.