Microfusion initiators were technological devices utilized by Starfleet in the 24th century.
In 2372, a group of rogue Jem'Hadar conducted a raid on Deep Space 9, stealing microfusion initiators, photonic amplifiers, and EPS power stabilizers, intending to use the devices to restore an Iconian gateway which had been discovered by the Dominion in the Gamma Quadrant. (DS9: "To the Death")
In 2373, Miles O'Brien was unable to find any microfusion initiators aboard a Jem'Hadar fighter that had crashed on Torga IV. (DS9: "The Ship")