The present invention relates to a percussion hammer for enlarging drilled holes. In spite of statistical variations in length and other factors among the fibers, there are frequencies at which the amplifiers produce nearly coherent outputs. A dual phase high strength steel product is made having a uniform coating of zinc in spite of the high manganese content of the steel. The mating structure of the first substrate is moved into a confronting relationship with the mating structure of the second substrate or wafer.