This is the eight-voice backplane bare board designed for use with crOwBX voice cards. The board is optimized for use with rev2.1 (or later) voice cards, but it can support rev2.0 crOwBX voice cards as well as vintage OBX voice cards when used with the optional crOwBX slot adapter boards (one per voice) Rev2.1+ cards do not require slot adapters. The crOwBX eight-voice backplane is fabricated to be extra heavy-duty. The board is 2.5mm thick with 2oz. copper layers and 5mm plated holes. Mounting holes are provided for all stress points making the board exceptionally robust against mechanical failure.