Class four droid
BX-series could be found within the fourth class droid designation.
Droids of the fourth class, also referred to as fourth-degree droids, were droid units specializing in both military applications and security.
Models
Within the fourth-degree designation were models such as B2-series super battle droids from Baktoid Combat Automata, in addition to tactical droids, and BX-series droid commandos; all were considered to be battle droids.
Characteristics
A majority of droids in the fourth class were not designed with programming that allowed verbal communication or interaction with organic lifeforms. An exception existed in the form of the KX-series security droid, although its capabilities were not as comprehensive when compared to a protocol droid. The abilities of protocol droids were comparable to the T-series and its successor, both of which were tactical droid types utilized by the Confederacy.