Complex sentence: Aftermarket caliber conversions exist in.40 S&W and 10 mm auto. Since these calibers have a similar bolt-face as the 9x19mm Parabellum round, the bolt does not need to be changed.
Split into simpler sentences: Aftermarket caliber conversions exist in.40 S&W and 10 mm auto as well. Since they also have the same bolt-face as the 9x19mm Parabellum round, the bolt doesn't have to be changed.