
Tucker and Lorian finetuning an injector assembly
An injector assembly was, as far as Terran technology was concerned, a crucial component of a starship's main propulsion systems. As the name suggests, the injector assembly was presumably comprised of an array of smaller components. The injector supplies a substance (possibly deuterium) into a vessel's warp core or impulse drive reactor as a function of the matter/antimatter annihilation which generates a ship's warp field and other power systems. When the crew of Enterprise NX-01 needed to arrive to meet Degra at a prearranged time and place but were too far away to get there on time, Lorian modified the Enterprise's injector assembly to reach up to warp factor 6.9 but at shorter intervals. (ENT: "E²")
Malcolm Reed made a joke of Trip Tucker when he asked to massage the injector assembly with his fingers. Reed referenced Tucker's relaxing neuro-pressure treatments with T'Pol. (ENT: "Rajiin")
The Son'a injector assembly[]

Simulated launch of a Son'a injector assembly
In 2375, an injector assembly was for the Son'a a crucial piece of equipment in order to harvest metaphasic radiation from the rings of the Ba'ku planet. That piece of equipment was to be launched from a specialty ship, the Son'a collector, right into the rings of Ba'ku where it was to be detonated by firing charges that would start a thermolytic reaction, the radiation of which to be collected by he collector. A simulation ran by AhdarRu'afo showed that it was a viable option. Nevertheless, launch and execution were prevented through the intervention of the USS Enterprise-E and its crew. In the process both collector and assembly were destroyed. (Star Trek: Insurrection)