A projection welder for welding a nut to one side of a work has a movable upper electrode and a stationary lower electrode provided with a removable electrode tip for receiving and holding thereon the nut against which the work is urged by the upper electrode so that the work and the nut are welded together. A tubular nut-centering pin projects upwardly from the upper surface of the electrode tip and is axially aligned with the upper and lower electrodes to receive the nut such that the pin engages with a threaded hole in the nut whereby the nut thus received on the nut-centering pin is centered relative to the upper and lower electrodes. The nut-centering pin has an axial through-hole connected to an air source under pressure so that air can be fed under pressure to portions of the work and nut being welded.
