the order of about 0 100 inches withthe components situated in the foregoing arrangement pneumatic piston 44 supplies the power while hydraulic piston 42 provides a constant speed fortraversing cartridge 12 past the electrodes whenever controller 46 is actuated by depression of operating button 62 with a voltage of about 8 66 kv and frequency of about 20 25 khz applied to the electrodes cartridges 12 are caused to be displaced by operation of the pistons in the corona emission path of the electrodes in order to ensure that an adequate energy level of charge is attained on the wall surface of holes 14 sufficient for enhancing the adhesive bond ofthe pins to the desired extent it has been found essential that the rate of rail travel during the application of charge be carefully controlled as measured prior to insertion of pins 16 advancing the tray 36 at a linear velocity on the order of about two inches per second or less produced surface energy levels in excess of 60 dynes cm similarly highertreating velocities on the order of between 3 0 to 3 5 inches per second reduced the surface energies to on the order of about 40 52 dynes cm in either event it.