Enrique asked me if he could use a No.4 oscillator on his SP15. The answer is yes. The tubes are the same diameter (3¾”) and the worm gear is the same part (DR-338), but the shaft and tube length of the SP15 is longer (13″) than the No. 4 (12½”). While the No. 4 shaft will fit on the SP15 it can laterally shift in the bracket. I suspect this might stress the form rollers. The SP15 oscillator does not fit in the No. 4 frame.