The Injector machines resemble bacteriophages; which are viruses that infect and reproduce within bacterium, sometimes destroying the bacterium. The bottom of the machines have drills on them and they stand on four legs. The structures sport a large red gem-like ornament on the very top.
The body of the rig itself seems to showcase a clear panel containing within it an organic heart, much like the Crystal Heart located in the center of the Crystal Temple. These seemingly organic hearts are attached to the head and feet of the machine via red and blue tubes that resemble arteries and veins respectively. Due to this, these machines can be considered biomechanical.
Due to the drill and viral shape of the machines, it is likely that they dig up gemstones found beneath the ground, and modify them into becoming Gems by sending them through the heart which will give them life. The Gem shaped recesses, from which Amethyst states is where she was "born," serve as an incubator for this process, akin to how phage type viruses, the shape of the machines, infect and utilize a cell, in this case, the Earth itself, to reproduce.
- In "The Return", Jasper refers to Amethyst as "an overcooked runt," which could imply that she was incubated longer than these machines intended her to be.
- In "On the Run", Amethyst refers to these as Old Gem Junk.
- As Peridot was activating the Kindergarten in "Marble Madness", she reports "Now accounting for all operational Injectors." As the Old Gem Junk (as Amethyst calls it) was the only objects there besides rock, and a good number seemed to be busted, it is extremely likely that Peridot was referring to the Old Gem Junk.