Book says 16,000. I had 32000 on two sets, and last set I put in the Iriduim NGKs at about six bucks a hole. Now it runs just as good as it did when I had the stock plugs with 32000. Starts just as easy, too.
If we want to get all the life out of a plug, I think we will have to put them in new machines to finish wearing them out.