an upturned edge 16 that is received within a downwardly opening groove 18 provided within the forward portion of upper frame member 12 the foregoing frame components are secured together by pin and screw type fasteners 20 22 23 of which only illustrative ones are shown in fig1 frame plate 14 has a plurality illustratively eight of laterally spaced parallel slots 24 which extend forwardly from the rear edge of plate 14 and pass under its upturned forward edge 16 slots 24 receive and constrain lateral movement of respective ones of a corresponding plurality of elongate ram or slider members 26 26 39 of which only illustrative ones are shown as is best shown in fig5 each slider 26 has an elongate lightweight body 28 that preferably is formed of injection molded plastic material and that has an impact surface 29 at its rear end the slider body supports at its forward end a hammer face 30 preferably formed of stamped sheet metal and has intermediate its length a plurality illustratively four of armature elements 32 preferably formed of chemically etched electrical steel coated with titanium nitride openings are also provided through slider body 28 for the purpose of further reducing its weight and or of receiving fastener and other components of module 10.