Are there any circumstances where ruby is not a good choice for a ball probe tip? Yes. In fact, there are two main circumstances in precision measurement when you should not use a ball probe tip made of ruby. The first involves adhesive wear. Adhesive wear occurs when a ruby ball probe is used to scan aluminum and is caused by two materials having a chemical attraction. In order to avoid this, when scanning aluminum you should use a ball probe made of silicon nitride. The second circumstance in which to avoid ruby is when abrasive wear is a risk. Abrasive wear occurs when scanning cast iron and is due to the small particles that cause scratches on the ball probe tip. Zirconia should be used instead of ruby to avoid abrasive wear when scanning cast iron.