400 B block

Sorry Bill...lol. I forgot yor part. I use the Dakota Ultrasonics PR-8. It isnt cheap. But honestly, cheap testers cannot be trusted. You want one that comes certified and that can be adjusted for the material being tested. There are different ways to test too. Cheap ones can usually do one type. either a spot test or a scan. Cheap ones also come with sample material blocks to set up the tester or pre-programmed frequencies. But iron is very different manufacturer to manufacturer. The cheap machines are about as accurate as a ruler for measuring spark plug gap.