I'm not sure why you would think it's threaded, unless you're looking at the back end of it where there is a slot for a screwdriver. That is for manually breaking up a jam. You know, like after those burrito dinners.
Most of them are very uncomplicated apparatuses, that resemble a water puppy pump inside. It's just a rubber impeller, with a small stainless "blade" forward of that to chew up the uh, well, tacos etc..