I have a set of hydraulic dent raisers, but I rarely use them.....the best "tool" I've found for the job is a set of screw in choke installation steel pilots....they come in .002" increments and can be driven under the dent....once properly located under the dent, a brass or plastic hammer can be used to finish the dent from the outside....often, a bit of bore honing is required to finish the job, since a dent will have caused a bit of metal stretching.