Abstract: An ultrasonic working apparatus including a booster horn defined by a coaxially aligned rod member and plate member. The rod member has one end thereof coupled to the vibrator by a rod coupler, and an opposite end portion coupled to one end of the plate member. The opposite end portion of the plate member is provided with a plurality of workpiece engaging lugs. The upper end of the plate member is substantially congruent with the lower end of the rod member. The plate member has a thickness at the distal end portion less than the thickness at the end thereof coupled to the rod member and has a width at the distal end substantially greater than the width of the end coupled to the rod member. The booster horn has a total axial length substantially equal to one-half the vibratory resonant wavelength. A support collar is provided about the lower portion of the rod member to provide a second support for the apparatus and defines a nodal position of the amplitude of the vibratory force transmitted therethrough.