Different generations of the at-x

@spife7980 is correct. The main differences between Gen 1 and Gen 3 are how you adjust the buttstock. Gen 1 uses bolts/screws that need an allen wrench, and Gen 3 is tool less. The atx also did not come with a folding hinge or forend bridge from the factory and had to be bought separately. The atxc includes both these items, and a re designed bolt and lighter action.