BX-series were fourth class droid
Droids of the fourth class, also referred to as fourth-degree droids, were droid units specialized in both military and security roles.
Among the fourth-degree models were Baktoid Combat Automata's B2-series super battle droids, tactical droids, and the BX-series droid commandos. These were all categorized as battle droids.
A common trait of fourth class droids was a lack of programming for verbal communication and interaction with organic lifeforms. However, the KX-series security droid presented an exception, although its communication abilities were not as sophisticated as those of a protocol droid. Protocol droids had capabilities on par with the T-series and its successor, which were tactical droid types utilized by the Confederacy.