Abstract: Mounting for ignition module in which a ferromagnetic flux carrying core includes a plurality of spaced, parallel leg portions. The ignition coil module has a generally central opening which is adapted to receive one of the core legs. A tapered slot is formed on one side of said coil module and is adapted to receive a correspondingly tapered bar portion of a synthetic plastic retainer. The retainer is an integral, thermoplastic block with a channel on the side opposite the tapered bar portion adapted to slide-fit about the inner edge portion of the core leg. A recess is provided in the leg of the core opposite the slot on said module. The retainer includes a frangible lug portion which is adapted to be displaced against the portion of the leg in which the recess is formed. Whereupon, when the lug is softened by ultrasonic energy, it flows into the recess and hardens therein while bonding to the contiguous portions of the retainer to fasten the module in fixed assembled relation on the core.