They worked on my engine cover bolts which were so rusty and worn I had to replace them so I could change the oil. One star deducted because the recommended drill size seems wrong. The instructions recommend a 1/4 bit for the #4 extractor, but after drilling, the extractor didn't catch - the hole was too big. I had to make the hole slightly larger with another drill bit and go to a #5 extractor/use an adjustable wrench to remove and it caught the edges perfectly and came out with ease. They seem to work really well, but the size of the drill can be confusing for people who have never worked with a set like this.