To the OP, you need to know that not all ultrasonic testers will read cast iron, so make sure the one you're looking at does. Also, the transducer doesn't HAVE to be curved. As long as it's a relatively small diameter (8mm is a popular size) so that all of the transducer surface will contact the cylinder, your readings will be accurate. There are some that come with several different shaped transducers, but they tend to be on the high end of budget.
